Backport the global styles variations changes from Gutenberg

[youknowriad]

This PR backports the global styles variations endpoint changes from the Gutenberg plugin.

Trac ticket: https://core.trac.wordpress.org/ticket/55505

[gziolo]

@oandregal and @jorgefilipecosta, we would appreciate your help here.

[youknowriad]

I think I managed to fix the tests, let's see what CI says.

[oandregal]

@youknowriad it looks like the only failing test is WP_Test_REST_Schema_Initialization::test_expected_routes_in_schema, which is missing one of the global styles routes.

[youknowriad]

I guess we need to regenerate that REST API fixtures file, I forgot how to do that. I can the entry manually though.

[oandregal]

This is working as expected for me.

This is what I've done to test:

Created a styles folder within src/wp-content/themes/twentytwentytwo with two files.

bluish.json whose content was:

{
  "version": 2,
  "title": "Blue style",
  "styles": {
    "color": {
      "background": "blue",
      "text": "white"
    }
  },
  "settings": {
    "color": {
      "palette": [
        { "slug": "blue", "name": "Blue", "color": "blue" }
      ]
    }
  }
}

redish.json whose content was:

{
  "version": 2,
  "title": "Red style",
  "styles": {
    "color": {
      "background": "red",
      "text": "white"
    }
  },
  "settings": {
    "color": {
      "palette": [
        { "slug": "red", "name": "Red", "color": "red" }
      ]
    }
  }
}

Then, I opened the site editor and, in the console, executed this command: wp.apiFetch({path: '/wp/v2/global-styles/themes/twentytwentytwo/variations', method: 'GET'}). Once the request is resolved I saw the content of the style variations.

I've also tested with the existing TwentyTwentyTwo theme with no styles folder and also works fine (the endpoint returns 0 style variations).

[youknowriad]

@gziolo Should I go ahead and commit this one?

[gziolo]

@gziolo Should I go ahead and commit this one?

That would be fantastic, thank you 🙇🏻

[youknowriad]

committed in https://core.trac.wordpress.org/changeset/53072