Themes: Add a Block Themes filter in Theme Install Screen.

The Theme Directory on wordpress.org recently got updated to show a shortcut for filtering block themes. This changeset adds a "Block Themes" filter when adding a new theme from WordPress administration.

It also introduces two new action hooks: `install_themes_pre_blockthemes` (fires before the tab is rendered) and `install_themes_blockthemes` (fires at the top the tab).

Follow-up to [meta11963].

Props luminuu, audrasjb, SergeyBiryukov, rafiahmedd.
Fixes #56283.
See #meta6330.


git-svn-id: https://develop.svn.wordpress.org/trunk@53906 602fd350-edb4-49c9-b593-d223f7449a82

src/js/_enqueues/wp/theme.js

@@ -1694,7 +1694,18 @@ themes.view.Installer = themes.view.Appearance.extend({
 	browse: function( section ) {
 		// Create a new collection with the proper theme data
 		// for each section.
-		this.collection.query( { browse: section } );
+		if ( 'blockthemes' === section ) {
+
+			var request = { tag: 'full-site-editing' };
+
+			// Get the themes by sending Ajax POST request to api.wordpress.org/themes
+			// or searching the local cache.
+			this.collection.query( request );
+			return;
+
+		} else {
+			this.collection.query( { browse: section } );
+		}
 	},
 
 	// Sorting navigation.