firebase-ios-sdk

Support AB testing of Firebase In-App Messages (#5005)

* Parse out experiment payload for experimental FIAMs and store it on FIRIAMMessageDefinition

* Fix bugs in parsing experimental payload

* Add nullable experiment payload to FIAM message definition. Add method in FIRExperimenmtController to validate running experiments and call this when new messages are fetched from FIAM backend

* Add and document new ABT methods, update FirebaseInAppMessaging.podspec to depend on ABT

* Clean up deprecated public message initializers, add experiment payload to private initializers

* Activate experiment for experimental messages upon impression

* Clean up activateExperiment API

* Add experimental payload to all message definition initializers

* Add unit test coverage for new ABT methods

* Add test coverage for parsing experimental messages

* Verify experiment payload gets passed to message superclass

* Scripts/style.sh

* Update Podfile for UI test app to include AB Testing SDK

* Add back deprecated initializers for now, these are needed for the test app

* Test for non-nil experiment payload

* Use mutable array directly, better memory usage

* Bump ABTesting podspec version, depend on new ABT in FIAM

* Remove mentions of FIREventOrigins.h

* Remove experiment payload from public API, hide it in private

* Scripts/style.sh

* Fix comment indentation, allow for FIAM to depend on minor version updates of ABTesting

* Move ABTExperimentPayload import to private header