Automatically generate some mega demo that references every demo

[Geokureli]

Maybe we could write a script that generates a Project.xml that includes every asset and source, allowing us to compile every demo at once. this should speed up CI significantly, as demos take the most time, so much so that we only build 4 on cpp

It may require us to change each demo to have a specific namespace (or just each Main.hx) or perhaps rather than actually referencing each Main.hx we make a macro the references each file, in the same way that coverage tests do