DoIts shouldn't dirty Compiler-Core #973
- Compile DoIts in an extension protocol
- Add ProtocolAnnouncement>>#package which is extension-aware; this duplicates logic in CompiledMethod>>#package, so both should probably be refactored
- Fix CompiledMethod>>#package to return nil for non-existent extension packages
- Fix PackageStateObserver>>#onProtocolModification: to be extension-aware- Add test AnnouncementSubscriptionTest>>#testAddExtensionMethod, which verifies
 that adding an extension method does not dirty the package of the containing cl
ass