Merge branch 'feature/base_flutter_1.12_upgrade' into feature/base_flutter_1.12_upgrade_for_androidx

# Conflicts:
#	android/src/main/java/com/idlefish/flutterboost/Platform.java
#	android/src/main/java/com/idlefish/flutterboost/XFlutterTextureView.java
#	android/src/main/java/com/idlefish/flutterboost/containers/FlutterSplashView.java
#	example/android/gradle.properties