A new user right, `delete-redirect`, is added (not given to anyone
by default). At Special:MovePage, if attempting to move to a single
revision redirect that would otherwise be an invalid target (i.e.
doesn't point to the source page), the user is able to delete the
target.
Deletions are logged as `delete/delete_redir2`, and the move is
then logged normally as `move/move`, mirroring current delete and
move logging.
To allow for separate handling by Special:MovePage,
MovePage::isValidMove now returns a fatal status `redirectexists` if
the target isn't valid but passes Title::isSingleRevRedirect.
Otherwise, `articleexists` is returned (as previously). Other callers
that don't intend to treat single revision redirects differently
should treat `redirectexists` the same as `articleexists`.
Currently, this deletion (like normal delete and move) cannot be
done through the move api. Since the deletion is only valid when
moving a page, unlike for normal deletion, deleting redirects with
this right cannot be done via the delete api either.
Bug: T239277
Change-Id: I36c8df0a12d326ae07018046541bd00103936144
77781b08c7