Clean up Android Support Library references, drop dependency on androidx.legacy, & Android 4.4 and older code#2147

jkasten2 merged 14 commits intomainOneSignal/OneSignal-Android-SDK:mainfrom

clean-up-android-support-library-referencesOneSignal/OneSignal-Android-SDK:clean-up-android-support-library-referencesCopy head branch name to clipboard