Use accessors for ValueHandleBase::V; NFC

This changes code that touches ValueHandleBase::V to go through
getValPtr and (newly added) setValPtr.  This functionality will be
used later, but also seemed like a generally good cleanup.

I also renamed the field to Val, but that's just to make it obvious
that I fixed all the uses.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301518 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed