Remove typing.AwaitableGenerator

[srittau]

Part of #7580

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

trio (https://github.com/python-trio/trio)
- src/trio/_socket.py:218: error: Incompatible return value type (got "list[tuple[Literal[AddressFamily.AF_INET], SocketKind, int, str, tuple[str, int]] | tuple[Literal[AddressFamily.AF_INET6], SocketKind, int, str, tuple[str, int, int, int] | tuple[int, bytes]]]", expected "list[tuple[AddressFamily, SocketKind, int, str, tuple[str, int] | tuple[str, int, int, int] | tuple[int, bytes]]]")  [return-value]
- src/trio/_socket.py:218: note: "list" is invariant -- see https://mypy.readthedocs.io/en/stable/common_issues.html#variance
- src/trio/_socket.py:218: note: Consider using "Sequence" instead, which is covariant
- src/trio/_socket.py:247: error: Argument 1 to "to_thread_run_sync" has incompatible type "Callable[[bytes | str | None, bytes | str | int | None, int, int, int, int], list[tuple[Literal[AddressFamily.AF_INET], SocketKind, int, str, tuple[str, int]] | tuple[Literal[AddressFamily.AF_INET6], SocketKind, int, str, tuple[str, int, int, int] | tuple[int, bytes]]]]"; expected "Callable[[bytes | None, bytes | str | int | None, int, int, int, int], list[tuple[AddressFamily, SocketKind, int, str, tuple[str, int] | tuple[str, int, int, int] | tuple[int, bytes]]]]"  [arg-type]
- src/trio/_dtls.py:739: error: Incompatible types in assignment (expression has type "tuple[bytes, bytes]", variable has type "None")  [assignment]
- src/trio/_tests/test_highlevel_serve_listeners.py:148: error: Value of type "tuple[type[BaseException], BaseException, TracebackType | None] | tuple[None, None, None] | Literal[False]" is not indexable  [index]
- src/trio/_tests/test_highlevel_serve_listeners.py:149: error: Value of type "tuple[type[BaseException], BaseException, TracebackType | None] | tuple[None, None, None] | Literal[False]" is not indexable  [index]
- src/trio/_tests/test_socket.py:128: error: Argument 1 to "MonkeypatchedGAI" has incompatible type "Callable[[bytes | str | None, bytes | str | int | None, int, int, int, int], list[tuple[Literal[AddressFamily.AF_INET], SocketKind, int, str, tuple[str, int]] | tuple[Literal[AddressFamily.AF_INET6], SocketKind, int, str, tuple[str, int, int, int] | tuple[int, bytes]]]]"; expected "Callable[[str | bytes | None, str | bytes | int | None, int, int, int, int], list[tuple[AddressFamily, SocketKind, int, str, tuple[str, int] | tuple[str, int, int, int] | tuple[int, bytes]]]]"  [arg-type]
- src/trio/_tests/test_exports.py:36: error: Incompatible types in assignment (expression has type "type[typing._Protocol]", variable has type "type[typing_extensions._Protocol]")  [assignment]
- src/trio/_tests/test_exports.py:167: error: Unused "type: ignore" comment  [unused-ignore]
- src/trio/_core/_tests/test_instrumentation.py:40: error: Unsupported operand types for in ("Task | None" and "Container[Task]")  [operator]
- src/trio/_core/_tests/test_instrumentation.py:209: error: "Literal[False]" object is not iterable  [misc]
+ src/trio/_core/_traps.py:65: error: INTERNAL ERROR -- Please try using mypy master on GitHub:
+ https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
+ Please report a bug at https://github.com/python/mypy/issues
+ version: 2.4.0
+ src/trio/_core/_traps.py:65: note: use --pdb to drop into pdb
+ Traceback (most recent call last):
+   File "mypy/checker.py", line 781, in accept
+   File "mypy/nodes.py", line 1358, in accept
+   File "mypy/checker.py", line 5849, in visit_decorator
+     self.visit_decorator_inner(e)
+   File "mypy/checker.py", line 5870, in visit_decorator_inner
+     ret_type = self.named_generic_type("typing.AwaitableGenerator", [ty, tc, tr, t])
+   File "mypy/checker.py", line 7987, in named_generic_type
+     info = self.lookup_typeinfo(name)
+   File "mypy/checker.py", line 7994, in lookup_typeinfo
+     sym = self.lookup_qualified(fullname)
+   File "mypy/checker.py", line 8077, in lookup_qualified
+     raise KeyError(
+ KeyError: "Could not find builtin symbol 'AwaitableGenerator' (If you are running a test case, use a fixture that defines this symbol)"
+ 

starlette (https://github.com/encode/starlette)
+ .../projects/_starlette_venv/lib/python3.13/site-packages/trio/_core/_traps.py:65: error: INTERNAL ERROR -- Please try using mypy master on GitHub:
+ https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
+ Please report a bug at https://github.com/python/mypy/issues
+ version: 2.4.0
+ .../projects/_starlette_venv/lib/python3.13/site-packages/trio/_core/_traps.py:65: note: use --pdb to drop into pdb
- starlette/testclient.py:86: error: Unused "type: ignore" comment  [unused-ignore]
- starlette/testclient.py:87: error: Class cannot subclass "Response" (has type "Any")  [misc]
- starlette/testclient.py:155: error: Unexpected keyword argument "status_code" for "WebSocketDenialResponse"  [call-arg]
- starlette/testclient.py:155: note: "WebSocketDenialResponse" defined in "starlette.websockets"
- starlette/testclient.py:155: error: Unexpected keyword argument "headers" for "WebSocketDenialResponse"  [call-arg]
- starlette/testclient.py:155: error: Unexpected keyword argument "content" for "WebSocketDenialResponse"  [call-arg]
- starlette/testclient.py:199: error: Class cannot subclass "BaseTransport" (has type "Any")  [misc]
- starlette/testclient.py:373: error: Unused "type: ignore" comment  [unused-ignore]
- starlette/testclient.py:375: error: Unused "type: ignore" comment  [unused-ignore]
- starlette/testclient.py:379: error: Class cannot subclass "Client" (has type "Any")  [misc]
- starlette/testclient.py:432: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_testclient.py:267: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_testclient.py:268: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_templates.py:33: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_templates.py:34: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_templates.py:73: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_templates.py:74: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_templates.py:99: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_templates.py:100: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_templates.py:129: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_templates.py:130: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_templates.py:134: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_templates.py:135: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_templates.py:175: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_templates.py:176: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_requests.py:98: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_requests.py:119: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_requests.py:161: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_requests.py:180: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_requests.py:502: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_formparsers.py:300: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_formparsers.py:375: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_formparsers.py:399: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_formparsers.py:422: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_formparsers.py:686: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_formparsers.py:765: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_formparsers.py:795: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_formparsers.py:822: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_formparsers.py:851: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_formparsers.py:879: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_formparsers.py:909: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_formparsers.py:939: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_formparsers.py:956: error: Unused "type: ignore" comment  [unused-ignore]
- tests/test_formparsers.py:1002: error: Unused "type: ignore" comment  [unused-ignore]
+ Traceback (most recent call last):
+   File "mypy/checker.py", line 781, in accept
+   File "mypy/nodes.py", line 1358, in accept
+   File "mypy/checker.py", line 5849, in visit_decorator
+     self.visit_decorator_inner(e)
+   File "mypy/checker.py", line 5870, in visit_decorator_inner
+     ret_type = self.named_generic_type("typing.AwaitableGenerator", [ty, tc, tr, t])
+   File "mypy/checker.py", line 7987, in named_generic_type
+     info = self.lookup_typeinfo(name)
+   File "mypy/checker.py", line 7994, in lookup_typeinfo
+     sym = self.lookup_qualified(fullname)
+   File "mypy/checker.py", line 8077, in lookup_qualified
+     raise KeyError(
+ KeyError: "Could not find builtin symbol 'AwaitableGenerator' (If you are running a test case, use a fixture that defines this symbol)"
+ 

websockets (https://github.com/aaugustin/websockets)
+ .../projects/_websockets_venv/lib/python3.13/site-packages/trio/_core/_traps.py:65: error: INTERNAL ERROR -- Please try using mypy master on GitHub:
+ https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
+ Please report a bug at https://github.com/python/mypy/issues
+ version: 2.4.0
+ .../projects/_websockets_venv/lib/python3.13/site-packages/trio/_core/_traps.py:65: note: use --pdb to drop into pdb
+ Traceback (most recent call last):
+   File "mypy/checker.py", line 781, in accept
+   File "mypy/nodes.py", line 1358, in accept
+   File "mypy/checker.py", line 5849, in visit_decorator
+     self.visit_decorator_inner(e)
+   File "mypy/checker.py", line 5870, in visit_decorator_inner
+     ret_type = self.named_generic_type("typing.AwaitableGenerator", [ty, tc, tr, t])
+   File "mypy/checker.py", line 7987, in named_generic_type
+     info = self.lookup_typeinfo(name)
+   File "mypy/checker.py", line 7994, in lookup_typeinfo
+     sym = self.lookup_qualified(fullname)
+   File "mypy/checker.py", line 8077, in lookup_qualified
+     raise KeyError(
+ KeyError: "Could not find builtin symbol 'AwaitableGenerator' (If you are running a test case, use a fixture that defines this symbol)"
+