* SiteLookup interface is added, and SiteStore extends
it. (any SiteStore type hints can be changed to use
SiteLookup if all they need is lookup functionality)
* Memcached based SiteStore code is split from the
database SiteStore, and SiteSQLStore is deprecated.
If no caching is desired when using a SiteStore, then
use a SiteDBStore instance, instead of passing $source
parameter in SiteStore::getSite and SiteStore::getSites.
* SiteListFileCache renamed to FileBasedSiteLookup and
implements SiteLookup.
Bug: T77990
Change-Id: I36b599884c211580ea6806a8a190c65c4f9087cf
