* Fix bug where messages with `app_launch` as a trigger weren't being parsed correctly
* Add a call to display executor check for app launch messages upon completion of initial app launch message fetch.
* Verify that the check for app launch messages gets called on initial app launch fetch
* Whitespace fix
* Fix duplicated error codes in checkAndDisplayNextAppLaunchMessage
* Refactor out logic for looking into app launch/foreground trigger messages to share more code
* Whitespace fix
* 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