Refactor dwarfdump -apple-names output

Summary:
This modifies the dwarfdump output to align it with the new .debug_names
dump. It also renames two header fields to match similar fields in the
dwarf5 header.

A couple of tests needed to be updated to match new output. The changes
were fairly straight-forward, although not really automatable.

Reviewers: JDevlieghere, aprantl

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D42415

llvm-svn: 323641