[clang] [clang] Introduce `SemaCoroutine` (PR #92645)

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

Was there ever an RFC on this whole 'splitting up Sema' project?

I have my own reservations as well.

I think starting up from the easier bits is a risky proposition, as we might realize this whole thing will fail when we get to the harder parts.

I also think this can lead in the future to the same sort of problems overusing const got us in the first place: needing large amount of repetitive changes all around when a commonly used or deeply nested component starts depending on a larger chunk of Sema.

Also, this will further cement current design lines, without considering where we want to be in the future.

And lastly, it seems this will lead to large amounts of code churn without proportional benefit, impacting in-tree development as well as external projects.

https://github.com/llvm/llvm-project/pull/92645