[pdb] Add command line options for dumping individual streams and blocks

I ran into a situation where I wanted to print out the contents of
page 6 of a PDB as a binary blob, and there was no straightforward
way to do that.

In addition to adding that, this patch also adds the ability to dump
a stream by index as a binary blob, and it will stitch together all
the blocks and dump the whole thing as one seemingly contiguous
sequence of bytes.

llvm-svn: 281070