Move DisplayServer enums and typedefs to DisplayServerEnums

This will allow decoupling `display_server.h` from a number of headers in the
codebase which only require those enums and not all the DisplayServer API.

scene/gui/control.cpp

@@ -2882,7 +2882,7 @@ void Control::_window_find_focus_neighbor(const Vector2 &p_dir, Node *p_at, cons
 
 void Control::set_default_cursor_shape(CursorShape p_shape) {
 	ERR_MAIN_THREAD_GUARD;
-	ERR_FAIL_INDEX(int(p_shape), CURSOR_MAX);
+	ERR_FAIL_INDEX(int(p_shape), DisplayServerEnums::CURSOR_MAX);
 
 	if (data.default_cursor == p_shape) {
 		return;