metal: create renderer

include/panda_qt/main_window.hpp

@@ -129,6 +129,7 @@ class MainWindow : public QMainWindow {
 	// Tracks whether we are using an OpenGL-backed renderer or a Vulkan-backed renderer
 	bool usingGL = false;
 	bool usingVk = false;
+	bool usingMtl = false;
 
 	// Variables to keep track of whether the user is controlling the 3DS analog stick with their keyboard
 	// This is done so when a gamepad is connected, we won't automatically override the 3DS analog stick settings with the gamepad's state