Scheduler which executes actions on looper.AndroidSchedulers.mainThread() or null if default
should be used.RxAndroidSchedulersHook to use based on order of
precedence as defined in the RxAndroidPlugins class header.Scheduler which executes actions on the Android UI thread.RxAndroidSchedulersHook implementation as a global override of any
injected or default implementations.AndroidSchedulers instance.register methods in this class
default implementation