Don't merge types of resources

When doing reflection users care about the names of the variable, the
name of the type, and the name of the members.  Remove duplicates breaks
this because it removes the names one of the types when merging.

To fix this we have to keep the different types around for each
resource.  This commit adds code to remove duplicates to look for the
types uses to describe resources, and make sure they do not get merged.

However, allow merging of a type used in a resource with something not
used in a resource.  Was done when the non resource type came second.

This could have a negative effect on compile time, but it was not
expected to be much.

Fixes https://github.com/KhronosGroup/SPIRV-Tools/issues/1372.