Notes: Arm the mention kses allowance on REST note creation

[adamsilverstein]

What?

Fixes #80258. Follow-up to #79604. Arms the note mention kses allowance when a note is created through the REST API, so the <a class="wp-note-mention user-N"> markup survives saving for users without unfiltered_html.

Why?

The mention kses scoping added in #79604 never fires on the REST create path:

• WP_REST_Comments_Controller::create_item() only copies the type param into the prepared data after prepare_item_for_database() has applied rest_preprocess_comment, so gutenberg_notes_scope_mention_kses_rest() sees no comment type (and no id to resolve one from) and does not arm.
• create_item() then inserts through wp_insert_comment( wp_filter_comment( ... ) ) directly, never calling wp_new_comment(), so the preprocess_comment arm does not fire either.

As a result, creating a note with a mention as an author or contributor (or as anyone but a super admin on multisite) silently strips the mention classes, which breaks mention chips in the UI and, once #79606 lands, mention notifications.

How?

When the prepared data and the request id leave the comment type unknown, resolve it from the request's type param, which create_item() validates against core types before preparing.

Testing Instructions

1. As a user without unfiltered_html (e.g. an author) on a post they can edit, open the editor and add a note that @-mentions another user.
2. Save and reload: without this fix the mention renders as a plain link (classes stripped); with it the mention chip survives.

Regression tests: test_rest_prepare_arms_for_note_creation, test_rest_prepare_does_not_arm_for_regular_comment_creation, and test_mention_markup_survives_rest_note_creation_end_to_end fail without the fix and pass with it:

npm run test:unit:php:base -- --filter Tests_Notes_Mention_Kses

[github-actions]

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Co-authored-by: adamsilverstein <adamsilverstein@git.wordpress.org>
Co-authored-by: Mamaduka <mamaduka@git.wordpress.org>

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[github-actions]

Flaky tests detected in ce2f51e.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/29354680864
📝 Reported issues:

• [Flaky Test] adds and activates a new tab when pressing Enter at the end of a tab label #80106 in /test/e2e/specs/editor/blocks/tabs.spec.js

[Mamaduka]

Makes sense. Thanks, @adamsilverstein!