Make DisplayModeDirector aware of whether HBM is active

Currently DisplayModeDirector casts Vote.PRIORITY_HIGH_BRIGHTNESS_MODE
based on whether High Brightness Mode (HBM) is allowed, rather than
based on whether HBM is actually active. This can lead to cases where
the HBM refresh rate vote is cast when HBM is allowed but not actually
used.

This change corrects this behavior, and makes DisplayModeDirector check
that HBM is both allowed (enabled) and actually in use (active).

Bug: 200851199
Test: atest DisplayModeDirectorTest
    BrightnessLevelPreferenceControllerTest
    HighBrightnessModeControllerTest
Change-Id: I8cb8f023a6bca11de976866259032143f43d9a4f