VirtualDisplay API for brightness callback and default.

Any rate limiting will essentially result in the wrong brightness
passed to the display owner. The callback is ONLY invoked if the
display has an explicit default brightness, in practice there will
only be 1-2 such displays at a time.

Bug: 285020111
Test: presubmit
Test: CTS
Flag: android.companion.virtualdevice.flags.device_aware_display_power
Change-Id: Ie991cfc9a85cbd6711d6c67a6ae5b51ac35f2f59