Decouple RenderingServer from as much of the codebase as possible

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

editor/debugger/editor_debugger_node.cpp

@@ -51,6 +51,7 @@
 #include "scene/gui/menu_button.h"
 #include "scene/gui/tab_container.h"
 #include "scene/resources/packed_scene.h"
+#include "servers/display/display_server.h"
 
 template <typename Func>
 void _for_all(TabContainer *p_node, const Func &p_func) {