[vulkan] Switch deferred opaque attachment to f16 rgb

While looking at the deferred attachment images with using a template in
mind, I noticed that the opaque attachment was using 8-bit color. The
problem is, it's meant to be HDRI with the compose pass crunching it
down to LDRI. Switching to 16-bit float does seem to have made a subtle
difference (hey, it's still quake data, not much HDRI in there).

libs/video/renderer/vulkan/deferred.plist

@@ -77,7 +77,7 @@
 		};
 		opaque = {
 			imageType = `2d;
-			format = r8g8b8a8_unorm;
+			format = r16g16b16a16_sfloat;
 			samples = 1;
 			extent = {
 				width = $output.extent.width;