[clang] [Clang] Fix handling of explicit parameters in `SemaLambda` (PR #168558)

[Willem Kaufmann via cfe-commits]

WillemKauf wrote:

> > @AaronBallman Would you want a release note for this scale of change?
> 
> Yes (indicating the fixed issue)

Added release notes to `clang/docs/ReleaseNotes.rst`. I don't think the addition of a new attribute is "breaking" AST dumping, please correct me if I am wrong or if you have any feedback on the release notes!

Thanks all.

https://github.com/llvm/llvm-project/pull/168558