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.

Built from https://develop.svn.wordpress.org/trunk@53906


git-svn-id: http://core.svn.wordpress.org/trunk@53465 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/theme-install.php

@@ -96,8 +96,10 @@ if ( $tab ) {
 	 *  - `install_themes_pre_search`
 	 *  - `install_themes_pre_updated`
 	 *  - `install_themes_pre_upload`
+	 *  - `install_themes_pre_blockthemes`
 	 *
 	 * @since 2.8.0
+	 * @since 6.1.0 Added `install_themes_pre_blockthemes`.
 	 */
 	do_action( "install_themes_pre_{$tab}" );
 }
@@ -185,6 +187,7 @@ require_once ABSPATH . 'wp-admin/admin-header.php';
 		<ul class="filter-links">
 			<li><a href="#" data-sort="popular"><?php _ex( 'Popular', 'themes' ); ?></a></li>
 			<li><a href="#" data-sort="new"><?php _ex( 'Latest', 'themes' ); ?></a></li>
+			<li><a href="#" data-sort="blockthemes"><?php _ex( 'Block Themes', 'themes' ); ?></a></li>
 			<li><a href="#" data-sort="favorites"><?php _ex( 'Favorites', 'themes' ); ?></a></li>
 		</ul>
 
@@ -269,8 +272,10 @@ if ( $tab ) {
 	 *  - `install_themes_search`
 	 *  - `install_themes_updated`
 	 *  - `install_themes_upload`
+	 *  - `install_themes_blockthemes`
 	 *
 	 * @since 2.8.0
+	 * @since 6.1.0 Added `install_themes_blockthemes`.
 	 *
 	 * @param int $paged Number of the current page of results being viewed.
 	 */