[clang] [CIR][NFC] Upstream VectorType support in helper function (PR #142222)

[Henrich Lauko via cfe-commits]

xlauko wrote:

This partially ports my changes from https://github.com/llvm/clangir/pull/1626 I was originally waiting for other vector stuff to get merged so we don't conflict. Can you please mirror everything that is applicable from that PR?

https://github.com/llvm/llvm-project/pull/142222