[clang] [coroutines] Introduce [[clang::coro_return_type]] and [[clang::coro_wrapper]] (PR #71945)

[Chuanqi Xu via cfe-commits]

================
@@ -7482,3 +7482,54 @@ generation of the other destruction cases, optimizing the above `foo.destroy` to
 
   }];
 }
+
+
+def CoroReturnTypeAndWrapperDoc : Documentation {
+  let Category = DocCatDecl;
+  let Content = [{
+The ``coro_return_type`` attribute should be marked on a C++ class to mark it as
----------------
ChuanqiXu9 wrote:

```suggestion
The `[[clang::coro_return_type]]` attribute is used to help static analyzers to recognize coroutines from the function signatures.

The ``coro_return_type`` attribute should be marked on a C++ class to mark it as
```

I'll feel better if I can see the motivation in the very beginning.

https://github.com/llvm/llvm-project/pull/71945