Why:
* Following T345578, the ActorStore throws an error on
attempting to create an actor whose name is their IP address
if temporary accounts are enabled.
* For the specific case of importing old revisions, we need to
be able to create new actors whose name is their IP address,
while still generally disallowing it.
What:
* Add $allowCreateIpActors flag to ActorStore, and check for
it during actor name validation.
* Set the flag from ActorStoreFactory::getActorStore depending
on whether temporary users are enabled.
* Add ActorStoreFactory::getActorStoreForImport, which sets
flag to true.
* Add RevisionStoreFactory::getRevisionStoreForImport, which
uses getActorStoreForImport. Use this from classes handling
imports, so that IP actors can always be created.
* Add $forImport flag on ActorMigration, since RevisionStore
uses an actor store obtained via ActorMigration.
Bug: T354207
Change-Id: I0715bd0d23089fd8156e579913e6e823089809be
6909b2016e