Editor: Register the core entity fields on the server

[jorgefilipecosta]

Backports the PHP of WordPress/gutenberg#84696, a follow-up to the entity fields API that landed in r64528.

Gutenberg registers the core fields (title, author, status, the media fields…) on the server, through the entity fields API, and the editors read them from /wp/v2/entity-fields. Core has the API but registers no fields yet, so the title column of the site editor's pages list is blank. This PR makes Core register them.

This PR:

• Copies the PHP files of @wordpress/core-fields from the Gutenberg build to wp-includes/build/scripts/core-fields/, in the gutenberg-php copy task that copies routes.php and pages.php, and loads its index.php from wp-settings.php the same way.
• Makes the existing entity fields tests replace the core fields with their fixture defaults, so they keep testing the API alone.
• Ports the tests of wp_register_core_field_collections() and wp_register_core_post_type_supports_fields().

Some notes:

• This needs a Gutenberg pin that includes Core fields: Register the default fields of WordPress on the server gutenberg#84696, which comes in its own PR along with the files it generates. Until then wp-includes/build/scripts/core-fields/ doesn't exist, so the new tests are skipped and nothing is registered.
• The pin also needs Core Actions, Core Fields: Translate the labels with the default text domain gutenberg#85139, which removes the gutenberg text domain from the labels, so they are translated with the default one. The test_the_labels_are_translated_with_the_default_text_domain test covers it.
• The media editor shows only the date and author of the attachment fields: the form that lists the rest (title, alt text, caption, description, file details) comes from the attachment view config Gutenberg added in Editor: Read the entity fields from the server gutenberg#84700, which Core doesn't have yet.
• It touches the same lines of Gruntfile.js and wp-settings.php as Editor: Register the core entity actions on the server #14509, which does the same for the core actions; whichever lands second needs a trivial rebase.

Testing Instructions

1. Set gutenberg.sha in package.json to trunk, then run npm run gutenberg:download and npm run build:dev.
2. Open wp-admin/site-editor.php?p=%2Fpage and verify the pages list shows the titles, authors, and statuses of the pages.
3. In the console, run await wp.apiFetch( { path: '/wp/v2/entity-fields?kind=postType&name=page' } ) and verify it returns the fields of pages with the @wordpress/core-fields/post_type_supports and @wordpress/core-fields/page modules.
4. Open the templates and patterns screens of the site editor and verify their titles, descriptions, authors, and sync statuses.
5. Open a post in the post editor and verify the document sidebar shows its status, publish date, slug, author, template, discussion, and format.
6. In the same post, add an Image block with an uploaded image, click "Edit image" in its toolbar, and open the "Details" tab: it shows the date added and the author.
7. Run npm run test:php -- --group entity-fields.

Gutenberg PR: WordPress/gutenberg#84696

Trac ticket: https://core.trac.wordpress.org/ticket/66229

Use of AI Tools

AI assistance: Yes
Used for: porting the code and the tests from the Gutenberg PR, and drafting this description; reviewed and edited by me.

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

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[github-actions]

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Props jorgefilipecosta, oandregal.

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[oandregal]

I've tested this as part of #14514

[github-actions]

A commit was made that fixes the Trac ticket referenced in the description of this pull request.

SVN changeset: 64581
GitHub commit: e205f82

This PR will be closed, but please confirm the accuracy of this and reopen if there is more work to be done.