fix(navigation): an omitted clause keeps the stored value (mendixlabs/mxcli#1522)

[ako]

Fixes the partial-navigation part of mendixlabs#1522 (#1404). The maintainer decided that an omitted clause keeps its stored value, as the menu, PWA and sync-error clauses already do.

The bug

navPatchWebProfile (mdl/backend/modelsdk/navigation_write.go) always wrote the home page, the role-based home pages, the login page and the not-found page from the statement, so any of them the statement left out was cleared. On a profile with a home page, create or modify navigation Responsive { menu item 'B' (...) }; removed the home page, and mx check then gave CE0527 "Select a default home page for this profile". navPatchNativeProfile did the same for role-based native home pages.

Fix

• Omitted fields are kept: each field is written only when the statement states it.
• Role home pages: home … for <role> replaces only that role's home page. Roles the statement does not mention keep theirs (navMergeRoleHomes, case-insensitive role match).
• Copy, not in place: both writers patch a copy of the stored profile. The helper used to change the document in place, and one existing test only passed because of that.
• Docs: the contradictory texts are fixed ("fully replaces" vs "omitting the block leaves it alone"):
  • syntax help navigation.create;
  • the manage-navigation, choose-edit-mode and migrate-design-prototype skills;
  • docs-site: alter-navigation.md, navigation-profiles.md and the quick reference;
  • the executor comment.

Tests

• TestUpdateNavigationProfile_OmittedClausesKeepStored
• TestNavPatchWebProfile_StatedClausesReplace
• TestNavPatchNativeProfile_OmittedRoleHomesKeepStored

Revert check: the tests fail with the fix reverted and pass with it restored.

Measured with mx check

A menu-only statement on a profile that has a home page went from CE0527 (1 error) to 0 errors, on both 11.15.0 and 11.6.6. The bug test mdl-examples/bug-tests/1522-navigation-omitted-clause-keeps-stored.mdl gives CE0527 with the old binary and 0 errors with the new one.

Open questions

1. No way to clear: MDL has no clause that clears a home page, login page, not-found page or one role's home page. Now that leaving a clause out keeps it, nothing can clear these. Add a clearing syntax?
2. create or replace navigation follows the same keep-what-is-omitted rule as create or modify, because the parser has always treated them the same. Should replace instead replace everything?

Also: a finding file. make build, make test, make lint and make check-findings pass. Not in this PR: the glyph part (separate PR) and the check for a home page a role cannot open (1404 c).

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