Update hook's names from global_styles_* to theme_json_*

[oandregal]

What?

In #44015 we've added a few hooks to filter the theme.json data at the different layer levels. This PR proposes that we rename them:

• global_styles_default => theme_json_default
• global_styles_blocks => theme_json_blocks
• global_styles_theme => theme_json_theme
• global_styles_user => theme_json_user

Why?

Because we're not filtering "global styles" but a specific part of it: the theme.json data it takes as input. The new names make this clearer. We also leave the global_styles_ prefix free for the future, in case we want to offer other kind of filters.

How?

• Renames the filters.
• Updates the docs.

Testing Instructions

Use the filters to modify some of the data. For example, this is how the theme data can be modified:

<?php

function filter_theme_json_theme( $theme_json ){
        $new_data = array(
                'version'  => 2,
                'settings' => array(
                        'color' => array(
                                'text'  => false, /* disable text color UI */
                                'palette'    => array( /* New palette */
                                        array(
                                                'slug'  => 'foreground',
                                                'color' => 'red',
                                                'name'  => 'Foreground',
                                        ),
                                ),
                        ),
                ),
        );
        return $theme_json->update_with( $new_data );
}
add_filter( 'theme_json_theme', 'filter_theme_json_theme' );

[jorgefilipecosta]

LGTM 👍

[oandregal]

This only updates the names of the filters. I'm undecided as to whether we should rename the "Global Styles Filters" page to "Theme.json Filters". Because it's published to the block editor handbook already, renaming it requires asking someone from the meta team to remove the old one. As it is also works fine if we want to add new filters later, so I lean towards maintaining what we have.

[oandregal]

These changes are being backported as part of WordPress/wordpress-develop#3247

[bph]

@c4rl0sbr4v0 Shall this be moved to milestone 14.1, so you can cherry-pick for the 14.1 release tomorrow?

[cbravobernal]

Cherrypicked for 14.1

[ockham]

I just cherry-picked this PR to the wp/6.1 branch to get it included in the next release: 6d76c1b