[llvm] [llvm/llvm-project][Coroutines] Move the SuspendCrossingInfo analysis helper into its own header/source (PR #106306)

[Tyler Nowicki via llvm-commits]

TylerNowicki wrote:

> This patch looks good. And the proposal looks good generally (it is long and maybe I missed some details).
> 
> But the problem is.. it looks like the contents of the PR is less related to the message body. It may be confusing. And also, I think such proposal should be sent to https://discourse.llvm.org/ to get a wider visibility. 

Can I take this as a lgtm with the changes to the PR and RFC? 

https://github.com/llvm/llvm-project/pull/106306