For efficient bulk querying, this means that
ApiQueryBase::showHiddenUsersAddBlockInfo() needs to return everything
needed by DatabaseBlock::newFromRow().
Since we're rewriting it anyway, we may as well also move
ApiQueryBase::showHiddenUsersAddBlockInfo() out into a trait of its own.
Bug: T232021
Change-Id: I9c5b17a232ecbfbffefc7e40608cf5684ce8a644
