[llvm] [CodeGen][Spill2Reg] Initial patch (PR #118832)

[via llvm-commits]

vporpo wrote:

Changed TII function names `spill2RegInsertToVectorReg()` to `spill2RegInsertToS2RReg()` and `spill2RegExtractFromVectorReg()` to `spill2RegExtractFromS2RReg()`. Rebased.

https://github.com/llvm/llvm-project/pull/118832