Support for LEDs without backing SVG

[danngreen]

See make_element.cc:

metamodule/firmware/vcv_plugin/src/make_element.cc

Lines 116 to 128 in afd2f66

	std::string_view get_led_image_by_size(rack::widget::Widget const *widget) {
	auto size = to_mm(widget->box.size.x);
	std::string_view image = size <= 2.6f ? "rack-lib/SmallLight.png" : //4px => 2.14mm
	size <= 3.7f ? "rack-lib/MediumLight.png" : //6px => 3.21mm
	size <= 4.5f ? "rack-lib/Light8px.png" : //8px => 4.28mm
	size <= 5.3f ? "rack-lib/LargeLight.png" : //9px => 4.82mm
	size <= 6.5f ? "rack-lib/VCVBezelLight.png" : //11px => 5.89mm
	size <= 18.f ? "rack-lib/VCVBezel.png" : //14px => 7.5mm
	"rack-lib/Rogan6PSLight.png"; //44px
	return image;
	}

The widget box size is used to find a SVG that's a similar size since as it is now, MetaModule::LightElement needs an image.
Instead we could have a MetaModule::LightElement have a diameter field which is used to draw and redraw the light. If the image field is present, then that's used. If not, then the diameter field is used.