Let InputDispatcher handle its own thread

We move the threading logic from InputManger to InputDispatcher by
removing dispatchOnce() method from InputDispatcherInterface and adding
a start() and stop() method in its place.

Bug: 130819454
Test: atest inputflinger_tests
Test: Touch input works on crosshatch
Change-Id: I1d06be2330a2f8b9261fd5c5323a486d6aa544e8