[clang] [Sema] Preserve ContainsUnexpandedParameterPack in TransformLambdaExpr (PR #86265)

[Younan Zhang via cfe-commits]

zyn0217 wrote:

Thanks for the review! I've just merged it.

> We should probably backport that

SGTM but given that this bug persists in so many versions, I think it is also fine to leave the fix just on trunk - especially since this is actually a partial fix.

We could issue a backport to 19 after we have addressed remaining FIXMEs i.e. bugs on attributes/constraints/captures, if I can catch up the release schedule. WDYT?

https://github.com/llvm/llvm-project/pull/86265