[llvm-pdbutil] Create a "bytes" subcommand.

[llvm-pdbutil] Create a "bytes" subcommand.

This idea originally came about when I was doing some deep
investigation of why certain bytes in a PDB that we round-tripped
differed from their original bytes in the source PDB.  I found
myself having to hack up the code in many places to dump the
bytes of this substream, or that record.  It would be nice if
we could just do this for every possible stream, substream,
debug chunk type, etc.

It doesn't make sense to put this under dump because there's just
so many options that would detract from the more common use case
of just dumping deserialized records.  So making a new subcommand
seems like the most logical course of action.  In doing so, we
already have two command line options that are suitable for this
new subcommand, so start out by moving them there.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306056 91177308-0d34-0410-b5e6-96231b3b80d8