[clang] [libcxx] [clang-tools-extra] [llvm] [libcxx] adds ranges::fold_left_with_iter and ranges::fold_left (PR #75259)

[Konstantin Varlamov via llvm-commits]

var-const wrote:

> I see @var-const has "requested changes" set, but I feel we've addressed the one unresolved comment of his.

@EricWF In fact, this patch changed quite significantly since I last looked at it (based on your feedback, I believe), so I would have appreciated being able to do another round of review before this was merged.

https://github.com/llvm/llvm-project/pull/75259