Decouple RenderingServer from as much of the codebase as possible

Notably decouples it from:
- AccessibilityServer
- DisplayServer
- Viewport
- Window

scene/gui/code_edit.cpp

@@ -31,10 +31,12 @@
 #include "code_edit.h"
 #include "code_edit.compat.inc"
 
+#include "core/config/engine.h"
 #include "core/config/project_settings.h"
 #include "core/input/input.h"
 #include "core/object/class_db.h"
 #include "core/os/keyboard.h"
+#include "core/os/os.h"
 #include "core/string/string_builder.h"
 #include "core/string/translation_server.h"
 #include "core/string/ustring.h"