[CodeView] Reserve TypeDatabase records up front.

[CodeView] Reserve TypeDatabase records up front.

Most of the time we know exactly how many type records we
have in a list, and we want to use the visitor to deserialize
them into actual records in a database.  Previously we were
just using push_back() every time without reserving the space
up front in the vector.  This is obviously terrible from a
performance standpoint, and it's not uncommon to have PDB
files with half a million type records, where the performance
degredation was quite noticeable.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@302302 91177308-0d34-0410-b5e6-96231b3b80d8