[Halo] All BSPs are loaded in a map at once, leading to perf issues and z-fighting

[notfrying1pans]

For an example on the z-fighting, I believe these are the pre- and post-flood reveal bsps rendering at the same time in 343 Guilty Spark

This also leads to unused bsps, such as b40b5 in Assault on the Control Room, loading and looking strange as they have no lightmaps.

[magcius]

Yeah, this was a concern when we were adding them. We could add a Layers panel on the left like we do in some other games which lets you toggle between BSPs.