[clang] [Sema] Add lambda decltype((x)) semantics to blocks (#207355) (PR #207583)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

Because this relates to Objective-C feature behavior in other language modes, we'd generally like to see a signal from Apple that they're comfortable with the direction. FYI, I think @ahatanak is on vacation currently, so it might be a bit before we get feedback.

https://github.com/llvm/llvm-project/pull/207583