[libcxx-commits] [libcxx] [libc++] Introduce `__product_iterator_traits` and optimise `flat_map::insert` (PR #139454)

[Louis Dionne via libcxx-commits]

https://github.com/ldionne approved this pull request.

LGTM, thanks! I have a few minor comments and we should add a release note for this.

https://github.com/llvm/llvm-project/pull/139454