Moving MIRCanonicalizerPass vreg renaming code to MIRVRegNamerUtils so that it
can be reused in another pass (ie planing to write a standalone mir-namer pass).
I'm going to write a mir-namer pass so that next time someone has to author a
test in MIR, they can use it to cleanup the naming and make it more readable by
having the numbered vregs swapped out with named vregs.
Differential Revision: https://reviews.llvm.org/D67114
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@370985 91177308-0d34-0410-b5e6-96231b3b80d8
