[llvm-pdbdump] Improve consistency among subcommands.

The pdb2yaml and raw subcommands did something very
similar but with a different output format, and they
used a lot of the same command line options, but each
one re-implemented the command line option with slightly
different spellings / options.  This patch merges them
together into a single definition which is shared by
both subcommands.  This new syntax also allows for more
flexibility in the way debug subsections are dumped.

Differential Revision: https://reviews.llvm.org/D33996

llvm-svn: 305032