[llvm] Add metadata pointer regex substitution to MIR update script (PR #163253)

[via llvm-commits]

saxlungs wrote:

> I wonder there should be more test impacted by this? The CI result would test us

I assume the CI will trigger if I un-draft the PR? I just didn't want github to start automatically adding the maintainers for review until you guys had a look at it in case I missed something silly

https://github.com/llvm/llvm-project/pull/163253