Toolbar: Add adminbar link for new sites in network installs.

Add a link that allows network administrators to go to the new site page from the "New" menu in the adminbar. 

Props johnjamesjacoby, sabernhardt, joedolson, rajinsharwar, huzaifaalmesbah.
Fixes #41104.

git-svn-id: https://develop.svn.wordpress.org/trunk@57600 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/admin-bar.php

@@ -938,6 +938,7 @@ function wp_admin_bar_edit_menu( $wp_admin_bar ) {
  * Adds "Add New" menu.
  *
  * @since 3.1.0
+ * @since 6.5.0 Added a New Site link for network installations.
  *
  * @param WP_Admin_Bar $wp_admin_bar The WP_Admin_Bar instance.
  */
@@ -1008,6 +1009,17 @@ function wp_admin_bar_new_content_menu( $wp_admin_bar ) {
 			)
 		);
 	}
+
+	if ( is_multisite() && current_user_can( 'create_sites' ) ) {
+		$wp_admin_bar->add_node(
+			array(
+				'parent' => 'new-content',
+				'id'     => 'add-new-site',
+				'title'  => _x( 'Site', 'add new from admin bar' ),
+				'href'   => network_admin_url( 'site-new.php' ),
+			)
+		);
+	}
 }
 
 /**