Update ConfirmEdit to return Status object on AbortNewAccount hook

Requires core update I6ae34c0 to actually send the message key back
in the error response. On older MediaWiki versions, behavior should
remain unchanged.

Bug: 60008
Change-Id: If9cc08e44d1d2efacf817b8c6cbb2d71a4e8b692
Merge "Update ConfirmEdit to return Status object on AbortNewAccount hook"