Remove the DependencyResolver dependency from the StoreMigrator.

Instead inject it in through the `migrateIfNeeded` method, because this happens at a time where the SchemaIndexProvider
has just been initialised anyway, so there's no need for any pseudo late-binding tricks.
Merge pull request #3503 from chrisvest/2.2-dep-free-migrator

Remove the DependencyResolver dependency from the StoreMigrator.