The get_theme_item method should respect fields param

[spacedmonkey]

The get_theme_item method in the WP_REST_Global_Styles_Controller does not respect the fields param context filtering.

Trac ticket: https://core.trac.wordpress.org/ticket/54595

[hellofromTonya]

As WP_REST_Global_Styles_Controller is introduced in 5.9, moving this into the 5.9 milestone.

The test Tests_Rewrite::test_url_to_postid_custom_post_type failed in PHP 7.2 only, so I have re-run them to see if it was a random error/time based.

Would it be possible to put in some unit tests to ensure the change is working as expected?

Added unit tests.

@spacedmonkey These same changes will be needed in Gutenberg to avoid these changes from being overwritten during a backport update.

[hellofromTonya]

Marking ​PR 2027 for commit.

[spacedmonkey]

In 52374:

REST API: Ensure that the get_theme_item method should respect fields param.

Fix the get_theme_item method in the WP_REST_Global_Styles_Controller class to respect the fields param context filtering and to return links.

Props spacedmonkey, hellofromtonya, peterwilsoncc, costdev.
Fixes #54595.

Merged!