Before MovePageTest was skipped if the move was valid,
claiming we can't test actual moves. Now we can.
Additionally, use MediaTestTrait for file and repo
mocking.
Change-Id: Ie8a1edbdb2f22432919f03a60c2dacc5d4528615
In Core REST API MediaFileHandler, display a different error for
title not found vs file not found. Files may be unfindable even if
the title exists due to permission errors, or if they are missing
from the file system.
Bug: T238374
Change-Id: If49273b979291e284043f6251ad8d989a10defe1