We used to use the Binding decoration for this, but this method is
hopelessly broken. If no explicit MSL resource remapping exists, we
remap automatically in a manner which should always "just work".
MSL does not seem to have a qualifier for this, but HLSL SM 5.1 does.
glslangValidator for HLSL does not support this, so skip any validation,
but it passes in FXC.