* FIRInAppMessagingDisplayMessage and FIRInAppMessagingDisplayDelegate refactor + downstream changes
* More downstream changes from FIRInAppMessagingDisplayDelegate, calling through to app-side delegate from default display executor
* Add delegate property on FIRInAppMessaging
* Display SDK changes to pass through in app message with callbacks
* Headless SDK unit test refactoring
* Display test app downstream changes
* Pull in headless SDK in display app, no need to have this come in as a framework anymore
* Run scripts/style.sh
* Remove WIP test
* Refactor FIRIAMDIsplayExecutor to take an InAppMessaging object for testing
* Depend on FirebaseAnalyticsInterop in UI test app
* File imports for FIRInAppMessaging files
* Remove FirebaseInAppMessaging imports
christibbs