Docs: Add a @since note about new parameters with the spread operator added to function signatures.

Props jrf.
See #47678.
Built from https://develop.svn.wordpress.org/trunk@46451


git-svn-id: http://core.svn.wordpress.org/trunk@46249 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/plugin.php

@@ -430,6 +430,8 @@ function add_action( $tag, $function_to_add, $priority = 10, $accepted_args = 1
  *     $value = do_action( 'example_action', $arg1, $arg2 );
  *
  * @since 1.2.0
+ * @since 5.3.0 Formalized the existing and already documented `...$arg` parameter
+ *              by adding it to the function signature.
  *
  * @global array $wp_filter         Stores all of the filters
  * @global array $wp_actions        Increments the amount of times action was triggered.