[ORC] Add withResourceKeyDo method to ResourceTracker.

This method behaves the same as MaterializationResponsibility::withResourceKeyDo
(which now forwards to the new method): It locks the session while providing
access to the ResourceKey associated with the tracker.

Adding this method to ResourceTracker allows resources to be allocated and
tracked for a given MaterializationUnit prior to that MaterializationUnit being
materialized. E.g. Platforms can now track and remove initializers and other
symbols.