GpuService: Add cmdFeatureOverrides

Add 'cmd gpu featureOverrides' to output the current FeatureOverrides
that were parsed by FeatureOverrideParser.

The feature overrides are intended to be used by
getPlatformDisplayAngle() in a later CL, to modify the behavior of
ANGLE.

Bug: 372694741
Test: cmd gpu featureOverrides
Flag: com.android.graphics.graphicsenv.flags.feature_overrides
Change-Id: I04c142fc6e0fd920315e41b36954c45cf032afb3