[llvm] [LLVM][Coroutines] Perform HALO on "coro_must_elide" coroutines (PR #98974)

[Chuanqi Xu via llvm-commits]

ChuanqiXu9 wrote:

Every time we change the coroutine semantics in LLVM IR, https://llvm.org/docs/Coroutines.html . It is also helpful for the reviewers to understand what you're doing.

And also it will be helpful for reviewers to provide a high level design for this and a lower level introduction for what this patch does too.

https://github.com/llvm/llvm-project/pull/98974