Support multi-display for KEYCODE_HOME event

Thanks Wale for this super clever temp solution. (^_^)
Introduce DisplayHomeButtonHandler to make flags handled per display.
The changes are:
- Extend DoubleTapHomeTimeoutRunnable to DisplayHomeButtonHandler
- Move mHomePressed, mHomeConsumed, mHomeDoubleTapPedding into DisplayHomeButtonHandler to be its members
- Move home handling logic to handleHomeButton, which is a method in DisplayHomeButtonHandler
- Add a displayId - handler map to handle home keys per display

Bug: 115978725
Test: atest com.android.server.policy
Test: Manual - Press home on secondary display and verify if home
      activity launched on secondary display

Change-Id: Ie7b4c72c8f9ff46b20b0a94cf6c36ba7db777128