[clang] [Clang] Avoid transforming lambdas when rebuilding immediate expressions (PR #108693)

[Younan Zhang via cfe-commits]

zyn0217 wrote:

> In the future, it would be better to push the unrelated parts of the pr in separate NFC commits, for ease of review.

Oops, I thought that was not too large, so I refactored that along the way of the call... anyways, I'll be careful next time :)

https://github.com/llvm/llvm-project/pull/108693