REST API: Limit default templates and template part areas data access via index

[Mamaduka]

What?

The PR limits access to the default_template_part_areas and default_template_types values. They are now only available to logged-in users.

Why?

See https://core.trac.wordpress.org/ticket/62574#comment:16.

Testing Instructions

1. Open a post.
2. Confirm that the default_template_part_areas and default_template_types values are returned when you run the base entity data selector. Selector - wp.data.select( 'core' ).getUnstableBase();.
3. Open an incognito window.
4. Visit the test URL below (replace the domain with your local site).
5. Confirm that values are no longer provided in the REST response.

https://gutenberg.test/wp-json/?_fields=description%2Cgmt_offset%2Chome%2Cname%2Csite_icon%2Csite_icon_url%2Csite_logo%2Ctimezone_string%2Cdefault_template_part_areas%2Cdefault_template_types%2Curl%2Cpage_for_posts%2Cpage_on_front%2Cshow_on_front&_locale=user

Testing Instructions for Keyboard

Same.

Screenshot

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: Mamaduka <[email protected]>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.