objectcache: Add makeLocalServerCache() method

This bypasses the indirection of global wgObjectCaches config and
ObjectCache::newFromParams static methods, which don't do anything
in practice.

This solves the ExtensionRegistry use-case where it couldn't use
the service container, which in turn opens the path for
being able to deprecate absence of Config being passed to
ObjectCache::newFromParams(), which isn't possible right now because
ExtensionRegistry depended on being able to call it without that,
and that is a hard requirement because ExtensionRegistry isn't
allowed to use the service container.

Change-Id: Ic88da279662f33d3585cb2232358d6faf590b5b3