Add SOURCE_SENSOR to InputDevice API.

Add input device source type SOURCE_SENSOR to InputDevice API.
SOURCE_SENSOR is not used to identify KeyEvent or MotionEvent but it can
be used to classifiy an input device is sensor capable.

Bug: 170131554
Test: atest InputDeviceSensorManagerTest
Change-Id: Iae93a771e69dda1f7bb8577632ea48ca79189b30
Merged-In: Iae93a771e69dda1f7bb8577632ea48ca79189b30