Do not animate keyboard and button brightness.

Keyboard and button brightness are always set to assign values
immediately but were being passed through the animation process
anyways. This interfered with the state of the screen brightness
animation. Intercept keyboard and button brightness directives and
implement them immediately.

Also use actual screen brightness and value to determine when we
are dimming or brightening. Previously we were using the sensor
values to determine whether the action called for was to brighten or
dim. This looks at the actual screen brightness level to make that
determination. If the two values get out of sync it is better to rely
on the screen value than the sensor value.

Fixes bug 6626681.

Change-Id: I82158f5188ffb739e01f818ba88e79f03a405c58