Add ability to configure which renderers are used by love.graphics.

- Add t.renderers and t.excluderenderers love.conf fields. They can be an array of renderer names.
- Add --renderers a,list,of,renderernames and --excluderenderers more,renderers argument options.

src/modules/graphics/metal/Graphics.mm

@@ -2016,7 +2016,7 @@ bool Graphics::isPixelFormatSupported(PixelFormat format, PixelFormatUsageFlags
 	return (usage & flags) == usage;
 }
 
-Graphics::Renderer Graphics::getRenderer() const
+Renderer Graphics::getRenderer() const
 {
 	return RENDERER_METAL;
 }