[llvm-pdbdump] Allow pretty to only dump specific types of types.

Previously we just had the -types option, which would dump all
classes, typedefs, and enums.  But this produces a lot of output
if you only want to view classes, for example.  This patch breaks
this down into 3 additional options, -classes, -enums, and
-typedefs, and keeps the -types option around which implies all
3 more specific options.

Differential Revision: https://reviews.llvm.org/D31791

llvm-svn: 299732