DebugInfo: Pubtypes: Coelesce pubtype registration with accelerator type registration.

It might be possible to eventually use one data structure, but I haven't
looked at the exact criteria used for accelerator tables and pubtypes to
see if there's good reason for the differences between the two or not.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195696 91177308-0d34-0410-b5e6-96231b3b80d8