[llvm] [PassBuilder] VectorizerEnd Extension Points (PR #123494)

[Arthur Eubanks via llvm-commits]

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

sounds good, lgtm with nits

please update the description with the intended usage

grepping for `passes-ep-vectorizer-start` shows that llvm/test/Other/new-pm-O0-ep-callbacks.ll and llvm/test/Other/pass-pipeline-parsing.ll need tests

https://github.com/llvm/llvm-project/pull/123494