Implement KEYCODE_TV_POWER

For devices that are not Android TV devices and not connected to a TV via HDMI, KEYCODE_TV_POWER is ignored.
For the following Android TV devices, KEYCODE_TV_POWER is an alias of KEYCODE_POWER:
- Devices that don't support HDMI
- HDMI TV panel devices
- HDMI devices with POWER_CONTROL_MODE set to NONE
- HDMI devices with CEC control disabled
For all other HDMI devices, KEYCODE_TV_POWER is forwarded to the HDMI stack by calling toggleAndFollowTvPower(). For HDMI source devices, this results in
1. Toggling of the HDMI-connected TV power state over HDMI-CEC
2. The source device following the TV power state

Bug: 157402294
Test: adb shell input keyevent KEYCODE_TV_POWER, manually verified TV power toggle behavior on ADT3

Change-Id: I59cd3f2a5c2b7a551176ab40ef9c559ad502a974