REST API: Introduce the necessary endpoints for the font library.

This commits add three endpoints to retrieve and manipulate fonts in WordPress.
This commit also means that we now have a fully functional Font Library in the site editor.

Props get_dave, youknowriad, mmaattiiaass, grantmkin, swissspidy, mcsf, jorbin, ocean90.
See #59166.

git-svn-id: https://develop.svn.wordpress.org/trunk@57548 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/rest-api.php

@@ -391,6 +391,10 @@ function create_initial_rest_routes() {
 	// Navigation Fallback.
 	$controller = new WP_REST_Navigation_Fallback_Controller();
 	$controller->register_routes();
+
+	// Font Collections.
+	$font_collections_controller = new WP_REST_Font_Collections_Controller();
+	$font_collections_controller->register_routes();
 }
 
 /**