[LVI] Add an LVI printer pass to capture test LVI cache after transformations

Summary:
Adding a printer pass for printing the LVI cache values after transformations
that use LVI.
This will help us in identifying cases where LVI
invariants are violated, or transforms that leave LVI in an incorrect state.
Right now, I have added two test cases to show that the printer pass is working.
I will be adding more test cases in a later change, once this change is
checked in upstream.

Reviewers: reames, dberlin, sanjoy, apilipenko

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D30790

llvm-svn: 298542