Added AutoBrightnessFallbackStrategy

This is used as a fallback when the autobrightness is enabled, but the
lux has not become valid yet.

Bug: 338039567
Test: atest com.android.server.display.brightness
Test: Manually verifying the usage of AutoBrightnessFallbackStrategy
when expected

Change-Id: I64b53cc9f6275b101cf79934a5f3a8fcb45f0ae9
10 files changed