[PDB] Save one type record copy

Summary:
The TypeTableBuilder provides stable storage for type records. We don't
need to copy all of the bytes into a flat vector before adding it to the
TpiStreamBuilder.

This makes addTypeRecord take an ArrayRef<uint8_t> and a hash code to go
with it, which seems like a simplification.

Reviewers: ruiu, zturner, inglorion

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D31634

llvm-svn: 299406