Add a new InputClassifier stage

The new InputClassifier stage could be used for additional processing
of input events prior to sending them to InputDispatcher. The new flow
of events will be InputReader -> InputClassifier -> InputDispatcher.

Here, we are calling the InputClassifier HAL and setting the MotionEvent
classification appropriately.

Bug: 62940136
Test: override notifyMotion to add extra flags to NotifyMotionArgs for
certain types of input events.
Test: atest inputflinger_tests

Change-Id: I2f390dc69f587ea25a3be8e4b8d5a207a5d529bf