Update nullability of light sensor injection.

This changelist allows the light sensor to be null even if the binding
is present.

Test: SystemUI does not crash when running on devices with no light
      sensor
Test: atest AmbientLightModeMonitorTest
Flag: EXEMPT bugfix
Bug: 393222374
Change-Id: I90b746b3aab118f9fc90fc117fe31f188e7d93b9