*) Many existing liblights support notification brightness
control via the alpha channel but do not support similar
for the battery led.
*) 8f7a4559ab
introduced a dependency on light capability
LIGHTS_ADJUSTABLE_BATTERY_LED_BRIGHTNESS such that, when
set, it was assumed that the battery led brightness is
also liblights adjustable. It turned out that this
was not the case.
*) Create a new capability to allow devices to distinguish
whether their liblights supports adjustable brightness
control for notification and battery leds independently
of one another.
*) Document how brightness support works in LightsCapabilities.
*) Copy LightsCapabilities comments to the default lights config
to raise visibility.
Change-Id: Id95905f07128c78c6acacf3b60d71bb37f70bcfb
e703ff0a0b