System: Add a new throttler/pacer which can catch up on lost time

This can result in worse frame pacing, so if you have a decent machine
you'll probably want to turn on "display all frames" in display
settings.

But, it's sadly needed for Android.

src/core/system.h

@@ -153,6 +153,7 @@ bool RecreateGPU(GPURenderer renderer, bool update_display = true);
 
 void SingleStepCPU();
 void RunFrame();
+void RunFrames();
 
 /// Sets target emulation speed.
 float GetTargetSpeed();