[feature/avatars] Pass phpbb_user object to prepare_form_acp()

The phpbb_user object might be used for language variables. Pass it as a
function argument to prepare_form_acp() instead of using globals.

PHPBB3-10018

phpBB/includes/avatar/driver/interface.php

@@ -69,11 +69,13 @@ interface phpbb_avatar_driver_interface
 	/**
 	* Prepare form for changing the acp settings of this avatar
 	*
+	* @param phpbb_user $user phpBB user object
+	*
 	* @return array Array of configuration options as consumed by acp_board.
 	*        The setting for enabling/disabling the avatar will be handled by
 	*        the avatar manager.
 	*/
-	public function prepare_form_acp();
+	public function prepare_form_acp($user);
 
 	/**
 	* Process form data