Add 2 noop methods to WP_List_Table: ->column_default() and ->column_cb().

`WP_List_Table` is essentially an `abstract` class. Some of its methods throw `die()` warnings if they aren't overridden in a child class.

These noop methods wouldn't be `abstract`, because they are not required in subclasses. However, `WP_List_Table` can call these methods in its own method, `->single_row_columns()`, whether a subclass defined them or not.

See #30799.


git-svn-id: https://develop.svn.wordpress.org/trunk@31210 602fd350-edb4-49c9-b593-d223f7449a82

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

@@ -1033,6 +1033,10 @@ class WP_List_Table {
 		echo '</tr>';
 	}
 
+	public function column_default( $item, $column_name ) {}
+
+	public function column_cb( $item ) {}
+	
 	/**
 	 * Generates the columns for a single row of the table
 	 *