[llvm-pdbutil] Add the ability to dump the dependency tree for a type

Previously we had the -type-index option which would dump the record of
a single, but we had no way to follow the dependency graph backwards and
also dump all dependent types.

Having this option makes test-writing better, because we can limit the
test to only those records that are of importance for the thing we're
trying to test, which allows us to use things like CHECK-NEXT to reduce
fragility.

Differential Revision: https://reviews.llvm.org/D34899

llvm-svn: 306852