Dispatch input events to the TV input

TvInputManagerService now creates an InputChannel pair and passes one
end to the app and the other end to the service. Then the TvInputManager
in the app creates an InputEventSender around one end of the channel to
send events and the service creates an InputEventReceiver around the
other end of the channel to receive events.
Most of the newly added code here was borrowed heavily from the IME.

Change-Id: I0bd83847cba0033ccb6f4b6dad267ebeaf5e9c7c