Add ID to InputEvent.

The interaction between Java and native code for KeyEvent and
MotionEvent is different, so I used different arrangement to pass
sequence number across JNI that keeps the consistency with other
metadata.

Unfortunately this new ID doesn't have absolute uniqueness guarantee so
it can't replace InputEvent#getSequenceNumber() which is used with a
strict in-process uniqueness assumption. Therefore only convert systrace
related use to ID.

Also expose ID generator through a static function in InputEvent so that
everyone can use it. InputReader and InputDispatcher will use different
instances.

Bug: 144889238
Test: Build and run.
Test: atest FrameworksCoreTests:KeyEventTest
Test: atest FrameworksCoreTests:MotionEventTest
Change-Id: Icbdcaee1d98948c05484865a4e15e55161ecfa69