add way to ratelimit mouse input events

[ardera]

With mice that deliver events at 1000Hz, the platform thread (especially on slower embedded devices) might become overloaded with processing mouse events. There should be a way to limit the rate at which mouse events are processed, for example, only at 60Hz or 120Hz, possibly via a --mouse-ratelimit cmdline option or a MOUSE_RATELIMIT build arg.

Optionally input event processing could also be moved to a seperate thread since technically only the dispatching of the pointer events (to the flutter engine) needs to be done on the platform task thread.

Ideally the kernel would do this, and there's an option for that in the usbhid driver, but at least in my testing with a razer viper that option didn't really change anything. Even with a reboot, setting usbhid.mousepoll to 10 to do 100Hz polling resulted in evhz still reporting an avg rate of 980Hz.