let betterRenderer import the modules

The module file set moves to its own eu07_modules library: a target can
only consume C++20 modules by linking the target that owns them, and
betterRenderer is a separate add_library. Its project includes become
imports.

CXX_EXTENSIONS must match across the two - a BMI built with -std=c++20
is refused by a unit compiled with -std=gnu++20.

betterRenderer/renderer/source/environment.cpp

@@ -8,7 +8,7 @@
 #include "nvrenderer/nvrenderer.h"
 #include "nvrendererbackend.h"
 #include "nvtexture.h"
-#include "simulation/simulationenvironment.h"
+import eu07.simulation.simulationenvironment;
 #include "sky.h"
 
 int MaEnvironment::GetCurrentSetIndex() {