egl: Rewrite eglGetMscRateANGLE to avoid probes, handle multi-monitor, and fractional refresh rates
Here's a WIP patch to fix eglGetMscRateANGLE to not take 100ms+ to calculate the refresh rate, which led to severe WebGL performance regressions.
Still TODO: proper CRTC selection to handle multi-monitor scenarios correctly. The old code didn't do this properly either. (Neither does the corresponding GLX code, it seems...)
References: #6996 (closed)