Support cross-platform tool builds with CMake

[twostars]

As with #671, we want to start looking into porting tools for builds on other platforms. A lot of that issue applies as the blockers are almost exclusively engine-related.

However, I feel windowing will largely differ here.

So the way I see it, is we have 2 approaches:

1. Migrate the tools to use a new framework (like, for example, Qt).
2. Scrap the tools and rewrite them entirely in something new as they're too coupled with MFC to be useful (and largely don't behave well or are even updated and working as-is). If we did this, we could rework to use something like imgui, where functionally the entire thing will behave considerably differently.

Either way, it's a considerably massive undertaking which shouldn't be taken lightly.