FREESCAPE: Depth rendering based on the original implementation

[neuromancer]

This PR contains the on-going work to replace the current approach to compute depth information, from z-buffer to the painter's algorithm similar to the original implementation. Despite the freescape game are from an era where GPUs where not even invented, modern OpenGL have a lot of trouble to correctly render the levels correctly using their z-buffer. The reason for that is coplanar triangles produce z-fighting. There are many tricks to minimize it, but it is very hard to completely remove it. On the first game, Driller, this is not bad, but later games like Castle Master, it is very easy to note these artifacts.

The solution, is of course, follow the original implementation that sorted bounding boxes according some kind of distance. In this PR, we used the annotated assembly code from @santiontanon to reimplement it.

Let's see how it changed, these are screenshots from master playing Castle Master for ZX Spectrum:

And this is with the sorting code:

And finally, the original implementation (apologies for the low quality!)

Finally, regardless of the state, this PR should NOT merged before tagging of 3.0.0. It will be featured in 3.0.1.

[lephilousophe]

I have a quick question: do you still need to disable DEPTH_TEST everywhere?
It's guaranteed disabled by OpenGL spec so, if you don't use it anymore, you just don't need to touch it.

[neuromancer]

Good catch: yes, no need to disable it, except when it is enabled for some specific cases.

[sev-]

Sounds and looks logical to me

[neuromancer]

This PR is currently blocked by a few artifacts that I need to debug in the code, where the sorting results in boundind boxes that are not correct and very visible glitches.

[neuromancer]

@dhruv0154 kindly improved the debug console and fixed the outstanding artifacts. This PR will be in testing for a bit in case there are more artifacts and then merged.