* 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
* Rename fine-tuning methods to reflect size class rather than orientation
* Modify existing constraints to de-portrait tablet layout, need a card width for tablet now
* Further constraint tinkering, add identifiers for better auto layout debugging
* More constraints for "landscape" appearance in tablet. Looks good for every case except Thin Image, which blows up the height of the message card
* Fix fine tune layout methods to correctly fine tune for compact height and width
* Update layout constraint identifiers to match titles in document outline for easier debugging
* Revert superfluous method name changes for layout fine tuning methods
christibbs