List Tables/WP_Screen: in WP_Screen, add methods to store, retrieve, and render screen reader text, primarily used by list table screens.

These additions are based on an audit and recommendations by the Accessibility team. #a11y'all

Props afercia.
Fixes #32147.

Built from https://develop.svn.wordpress.org/trunk@34891


git-svn-id: http://core.svn.wordpress.org/trunk@34856 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/class-wp-comments-list-table.php

@@ -443,6 +443,8 @@ class WP_Comments_List_Table extends WP_List_Table {
 
 		$this->display_tablenav( 'top' );
 
+		$this->screen->render_screen_reader_content( 'heading_list' );
+
 ?>
 <table class="wp-list-table <?php echo implode( ' ', $this->get_table_classes() ); ?>">
 	<thead>