add local focus mode and input event injection API to Window

 - This enables keyboard navigation for window without focus.
 - FLAG_LOCAL_FOCUS_MODE puts window into local focus mode.
 - Application needs to put window in local focus mode, control focus, and
   inject events to make dpad navigation work.
 - Window in local focus mode does not interact with window manager or ime
   regarding focus related events.
 - Also renamed ViewRootImpl.dispatchKey to dispatchInputEvent to allow both key and touch events injection.

Change-Id: I8e8561f29e0dade3797fb7ae3ee7690e6b7f8895