Previously, we would always emit all of the render targets in the subpass.
This commit changes it so that we compact render targets just like we do
with other resources. Render targets are represented in the surface map by
using a descriptor set index of UINT16_MAX.
Both logic and indentation suggests that the ; were not intended here.
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>