Today, the Android embedding calls Display#getRefreshRate once at initialization to get the refresh rate, and then assumes that stays stable when talking to the VSync waiter.

This is actually incorrect, since modern devices can dynamically change refresh rates. However, repeatedly calling getRefreshRate can be slow on some phones (2.5-5ms measured on a Huawei Nova 3), and calling it every frame is expensive.

We should use the AChoreographer_registerRefreshRateCallback where it's available to more efficiently get the FPS rate. This will unblock using the vsync target time for flutter/engine#29727

@blasten @ds84182 FYI