Add support for GamePad api in ITvRemoteServiceInput.

Gamepad-specific API is a separtate input path from standard "remote"
service. Specifically it adds:
  - openGamepad that creates a virtual input device with
  gamepad-specific suport
  - send gamepad keys
  - send gamepad axis updates, which support joysticks, analog triggers
  and HAT axis (as an alternative to DPAD buttons).

Bug: 150764186

Test: atest media/lib/tvremote/tests/src/com/android/media/tv/remoteprovider/TvRemoteProviderTest.java

Test: flashed a ADT-3 device after the changes. Android TV Remote
      on my phone still worked in controlling the UI.

Merged-In: I49612fce5e74c4e00ca60c715c6c72954e73b7a3
Change-Id: I49612fce5e74c4e00ca60c715c6c72954e73b7a3
(cherry picked from commit 9b9f556a)