Add Missing REST API Filters to WP_REST_Global_Styles_Revisions_Controller

[vipulpatil]

This ticket is created in response to a Gutenberg GitHub issue raised by anton-vlasenko and confirmed by ramonjd here ​https://github.com/WordPress/gutenberg/issues/68327

The issue highlights that the WP_REST_Global_Styles_Revisions_Controller class is missing standard WordPress REST API filters, such as rest_revision_query and rest_prepare_revision. According to ramonjd, the omission was intentional initially, as the endpoint was new and evolving, and public APIs were not introduced prematurely.

However, now that ​https://github.com/WordPress/wordpress-develop/pull/5699 has been completed, it makes sense to add these filters to align with WordPress REST API conventions and ensure consistency.

Proposed Solution:

Add the missing filters to the WP_REST_Global_Styles_Revisions_Controller class.
Use unique filter names, such as rest_global_styles_query and rest_prepare_global_styles_revision.
Backport these changes to WordPress Core for parity with Gutenberg and to provide developers with consistent, extensible APIs.
This update will enhance developer experience and maintain consistency with other REST controllers across the WordPress ecosystem.

## Summary
This PR adds two standard WordPress REST API filters to the Global Styles Revisions controller: rest_global_styles_revision_query and rest_prepare_global_styles_revision.
Currently, WP_REST_Global_Styles_Revisions_Controller lacks the standard WordPress REST filters, likely an oversight since other revision controllers include them.

### Changes Proposed

• Adds rest_global_styles_revision_query filter for query modification
• Adds rest_prepare_global_styles_revision filter for response data modification

Trac ticket: https://core.trac.wordpress.org/ticket/62742

@Mamaduka Can you take a look at this PR 🙇

@anton-vlasenko Can you look at this PR.

Adds missing REST API filters to the WP_REST_Global_Styles_Revisions_Controller class for consistency with other REST controllers.

Changes Introduced

Adds rest_global_styles_query filter for customizing global styles revision queries.

Adds rest_prepare_global_styles_revision filter for modifying prepared revision data before the response.

References

Trac ticket: #62742

[rcorrales]

Tested the filters locally and confirmed both are working correctly:

Test command (in browser console while logged in to wp-admin):

fetch('/wp-json/wp/v2/global-styles/<id>/revisions', {
    headers: { 'X-WP-Nonce': wpApiSettings.nonce }
})
.then(r => r.json())
.then(data => console.log(data));

Tested filters

add_filter( 'rest_global_styles_revision_query', function( $args, $request ) {
    $args['posts_per_page'] = 1; // Modify query to return only one revision.
    return $args;
}, 10, 2 );

add_filter( 'rest_prepare_global_styles_revision', function( $response, $post, $request ) {
    $response->data['_test_filter_applied'] = true; // Modify response by adding a test field.
    return $response;
}, 10, 3 );

Both filters trigger correctly and can modify query parameters and response data.

[welcher]

Reviewed in the 6.9 bug scrub today. We're 1 week from RC 1 and this doesn't seem likely to be ready. I'm going to move it to Future Release.