input: Add option to toggle pointer icon when using stylus

* The visible pointer icon when hovering or drawing with the stylus is
  quite annoying when trying to actually draw with it. Turn it off by
  default and add an option to turn it on.

Change-Id: Ib7f23e8b69589e3f875d150caf05065b64676e44

Conflicts:
	services/input/InputReader.cpp
	services/input/InputReader.h
	services/jni/com_android_server_input_InputManagerService.cpp