SurfaceFlinger: fix calculation issues with refresh rate selection

 - Initialize BufferQueueCore::mFrameRate
 - Load BufferQueueLayer::mLatchedFrameRate value before using it
 - Fix a bug with LayerInfoV2 where a frequent layer needs to post at least
   FREQUENT_LAYER_WINDOW_SIZE buffers.
 - Fix casting issues in RefreshRateConfigs

Test: adb shell /data/nativetest64/libsurfaceflinger_unittest/libsurfaceflinger_unittest
Bug: 147516364
Change-Id: Ie6e93ef2f4dd3a030bfd0dbbf8018d96680d8bb3