SF: Unify onModeChanged and frameRateOverride callbacks into single callback

Bug: 399482301
Flag: com.android.graphics.surfaceflinger.flags.unify_refresh_rate_callbacks
Test: atest libsurfaceflinger_unittest
Test: atest FrameRateOverrideTest
Test: atest LocalDisplayAdapterTest
Test: TouchLatency verified that unified event is sent.

Change-Id: I543813b60cd3abc592542b58b66c3dfc0dcdf2b6