Standardise capabilities for wp_template, wp_template_part and wp_global_styles

[carlomanf]

Description

Closes #30892

Although I have #27632 open as a more ambitious permissions prototype, there has not been much attention on it and it's unlikely to be ready for 5.8.

Accordingly, this branch is intended as a smaller target that just cleans up some code without changing behaviour.

At the moment, all three of the FSE post types use edit_theme_options as a blanket capability. However, all of them are doing this in different ways:

• wp_template does a just-in-time update of the capability using the user_has_cap filter
• wp_template_part uses the default post capabilities, and relies only on the REST API permissions check
• wp_global_styles sets some of the capabilities directly on the post type object, but many of them are missing

This standardises all three post types to configure their capabilities in the same way.

How has this been tested?

Screenshots

Types of changes

Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

[github-actions]

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[jorgefilipecosta]

I think this function is not very useful as part of our public API so we should mark it as internal by saying In the comments that it is internal and prefixing it with "_".

Regarding the name I guess it can more specific _gutenberg_get_default_capabilities_for_fse_post_types.

[carlomanf]

Amended.

[carlomanf]

Superseded by WordPress/wordpress-develop#1267