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

[via cfe-commits]

cor3ntin wrote:

What is the goal here? there is a lot of code reuse in C++ and C. and having a file per feature is going to make thing worse (maintenance, unboarding, compile times).
There are a lot more low-hamging fruits we should do before considering that sort of split.

Wasm, AMD, Builtins,  pragmas, random objects which could be in headers ( NestedNameSpecInfo, ContextRAII, NameClassification, AccessCheckingSFINAE,  InstantiatingTemplate, SynthesizedFunctionScope, etc - I would recommend using Aliases so they are still functionally in Sema)

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