Docs: Fix the types for some properties and parameters that use the generic object type.

See #50768


git-svn-id: https://develop.svn.wordpress.org/trunk@49119 602fd350-edb4-49c9-b593-d223f7449a82

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

@@ -43,7 +43,7 @@ class WP_List_Table {
 	 * The current screen.
 	 *
 	 * @since 3.1.0
-	 * @var object
+	 * @var WP_Screen
 	 */
 	protected $screen;
 
@@ -1092,7 +1092,7 @@ class WP_List_Table {
 		 * Filters the list table sortable columns for a specific screen.
 		 *
 		 * The dynamic portion of the hook name, `$this->screen->id`, refers
-		 * to the ID of the current screen, usually a string.
+		 * to the ID of the current screen.
 		 *
 		 * @since 3.1.0
 		 *