Synchronize brightness change with frame update for hdr layers.

When the brightness changes while hdr layers are on screen, the dimming
ratio may also change based on ambient conditions, so HWC must
recomposite the scene with the new brightness value.

Bug: 210151839
Test: builds, boots
Change-Id: I4741b28d13f4528a7b5c9045bec7a5823e802935