Improves pretty printing of variable types in llvm-pdbdump

* Adds support for pointers to arrays, which was missing
* Adds some tests
* Improves consistency of const and volatile qualifiers
* Eliminates non-composable special case code for arrays and function by using
  a more general recursive approach
* Has a hack for getting the calling convention into the right spot for
  pointer-to-functions

Given the rapid changes happenning in llvm-pdbdump, this may be difficult to
merge.

Differential Revision: https://reviews.llvm.org/D31832

llvm-svn: 299848