Extract ScriptInstance to simplify includes

This allows to include script_instance.h directly in the
generated gdvirtual.gen.inc, and remove excessive includes
from the codebase.

This should also allow Resource to use GDVIRTUAL macros,
which wasn't possible previously due to a circular dependency.

core/debugger/engine_profiler.h

@@ -31,10 +31,8 @@
 #ifndef ENGINE_PROFILER_H
 #define ENGINE_PROFILER_H
 
-#include "core/object/ref_counted.h"
-
 #include "core/object/gdvirtual.gen.inc"
-#include "core/object/script_language.h"
+#include "core/object/ref_counted.h"
 
 class EngineProfiler : public RefCounted {
 	GDCLASS(EngineProfiler, RefCounted);