Make ASSIST launch VIS and add a new keycode for TV (ALL_APPS)

    - KEYCODE_ASSIST: Looks for default VIS in system partition
      and launches it.
    - Ensure foreground activity assist context extras are collected
      and sent to VIS.
    - KEYCODE_ALL_APPS: Sends Intent.ACTION_ALL_APPS. For TV,
      this targets default launcher package in system partition.

Test: Manual: ASSIST: adb shell input keyevent 219
Test: Manual: ALL_APPS: adb shell input keyevent 284
Test: also tested with --longpress for these keys
Test: Manual: Checked with dummy app populating overridden
      onProvideAssistData()
Test: Keypresses after overriding ALL_APPS and ASSIST
      on Nexus Remote

Bug: 37950079
Bug: 38496261
Change-Id: I96d9de67d4a442a8c6cb7feec28fc9aeb0dcbc18