Dump symbol record details in llvm-pdbdump

This makes use of the newly introduced `CVSymbolVisitor` to dump details
of each type of symbol record in the symbol streams.  Future patches will
bring this visitor based dumping to the publics stream, as well as
creating a `SymbolDumpDelegate` to print more information about
relocations etc.

Differential Revision: http://reviews.llvm.org/D20545
Reviewed By: ruiu

llvm-svn: 270585