Networks and Sites: Simplify the check for main site on Network Admin → Sites screen.

This replaces a site ID comparison when displaying action links in `WP_MS_Sites_List_Table::handle_row_actions()` with a dedicated function call, `is_main_site()`, for clarity.

Follow-up to [13918], [25125], [26120], [32644], [38814].

Props ecorica, spacedmonkey, SergeyBiryukov.
Fixes #58150.

git-svn-id: https://develop.svn.wordpress.org/trunk@55666 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/class-wp-ms-sites-list-table.php

@@ -732,7 +732,7 @@ class WP_MS_Sites_List_Table extends WP_List_Table {
 			__( 'Dashboard' )
 		);
 
-		if ( get_network()->site_id !== (int) $blog['blog_id'] ) {
+		if ( ! is_main_site( $blog['blog_id'] ) ) {
 			if ( '1' === $blog['deleted'] ) {
 				$actions['activate'] = sprintf(
 					'<a href="%1$s">%2$s</a>',