[llvm] [VPlan] Create and re-use ModuleSlotTracker for metadata printing. (PR #203982)

[Florian Hahn via llvm-commits]

fhahn wrote:

Rebased after landing https://github.com/llvm/llvm-project/pull/223952

> Should we forcefully regenerate CHECKs in all the tests now (either here or in the very next PR), or have to have those alias lines be modified gradually as the tests need to be updated by future patches?

I am not sure, I think having them in all tests may make them unnecessarily verbose and more prone to unrelated changes due to metadata renumbering. But I am not sure if there's a nice way to automatically exclude them w/o a custom filter

https://github.com/llvm/llvm-project/pull/203982