provide ScreenToWorld conversion

[ericoporto]

Currently there's no reverse screen to world function so to handle clicks, we can do it work if we are merely hitting billboards (eg. An AGS character) but we can't click in a position in a 3D map.

There's this guide on raytracing, I need to read it and see if the math enlightens me on how to provide this.

https://raytracing.github.io/books/RayTracingInOneWeekend.html#outputanimage