SF: Improve refresh rate testing for FrameStats

This is useful to catch issues in fallback FPS calculations (which will
be introduced soon).

Bug: 382769837
Test: LayerTypeTransactionTests/LayerTypeTransactionTest.RefreshRateIsInitialized
Flag: com.android.graphics.surfaceflinger.flags.deprecate_frame_tracker
Change-Id: Iab91022ac3bd5afe1fa0adec26ef37788b043f14