[llvm] [llvm/llvm-project][Coroutines] Move spill related methods to a Spill utils (PR #107884)

[Chuanqi Xu via llvm-commits]

https://github.com/ChuanqiXu9 approved this pull request.

I didn't check if they are strictly the same line by line. But I believe it is trivial code movement. So LGTM with removing the prefix `[llvm/llvm-project]`.

But it looks like there were some regression reports for the first issue. Please take a look before landing.

https://github.com/llvm/llvm-project/pull/107884