[clang] [C++20][Coroutines] Lambda-coroutine with operator new in promise_type (PR #84193)

[Yanzuo Liu via cfe-commits]

zwuis wrote:

> Would you like to give a brief introduction for your design. I didn't figure it out.

- The function signature of `__builtin_lambda_this()` is `void*()`.
- Sema part: if it is a non-staic lambda expression (similar with this PR), create an expression `static_cast<T>(__builtin_lambda_this())` instead of `CXXThisExpr`, where `T` is `MD->getThisType()`.
- Codegen part: handling `__builtin_lambda_this()` is similar with handling `CXXThisExpr` except that it uses `CXXABIThisValue` instead of `CXXThisValue`.

https://github.com/llvm/llvm-project/pull/84193