Add doc blocks to functions that are missing them.

If the function has no need for `@param` or `@return`, do an archeaological dig to find `@since`.

See #32444.


git-svn-id: https://develop.svn.wordpress.org/trunk@32672 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/plugin.php

@@ -1658,6 +1658,13 @@ function get_admin_page_title() {
 	return $title;
 }
 
+/**
+ * @since 2.3.0
+ *
+ * @param string $plugin_page
+ * @param string $parent_page
+ * @return string|null
+ */
 function get_plugin_page_hook( $plugin_page, $parent_page ) {
 	$hook = get_plugin_page_hookname( $plugin_page, $parent_page );
 	if ( has_action($hook) )