[llvm] [VPlan] Support live-ins without underlying IR in type analysis. (PR #80723)

[via llvm-commits]

https://github.com/ayalz approved this pull request.

Thanks for accommodating, this looks good to me, adding a couple of nits, worth explaining what CanonicalIVTy is used for, possibly along with a TODO to promote the temporary live-ins-w/o-underlying-value (which need it) into recipes.

https://github.com/llvm/llvm-project/pull/80723