Editor: Add author support to the wp_block post type

[fabiankaegy]

The wp_block post type doesn't register author support, so the REST API doesn't return a pattern's author. Patterns already store post_author, and the post type's capabilities already check it, so this only makes it visible to the editor.

The block inserter uses it to split the "My patterns" category into "Site patterns" (every pattern on the site) and "My patterns" (only the ones the current user created).

Gutenberg PR: ​https://github.com/WordPress/gutenberg/pull/84680
Core PR: ​https://github.com/WordPress/wordpress-develop/pull/14269

Adds author support to the wp_block post type, so the REST API returns each pattern's author. The block inserter uses it to split the "My patterns" category into "Site patterns" (every pattern on the site) and "My patterns" (only the ones the current user created).

The author is already stored on every pattern and the post type's capabilities already check it. This only makes it visible to the editor.

Gutenberg PR: ​https://github.com/WordPress/gutenberg/pull/84680

Use of AI Tools

Drafted with Claude Code, reviewed by me.

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Thanks @t-hamano! Added tests for all four:

• The blocks controller returns author, and author / author_exclude filter patterns by author.
• An author can't change a pattern's author (403), an editor can.
• Deleting a user without reassigning deletes their patterns, and reassigning moves them. Worth noting: only posts and pages go to the trash, so the patterns are deleted permanently. Happy to set delete_with_user to false instead if we'd rather keep today's behavior.
• Regenerated the QUnit fixtures.