[clang] [libc++] Implement ranges::iota (PR #68494)

[James E T Smith via cfe-commits]

jamesETsmith wrote:

Sorry for the delay, just circling back to this. @philnik777 should I update the `robust_against_*` tests in both `test/std/algorithms` and `test/libcxx/algorithms/`? 

Probably a simple follow-up question, but you're interested in adding `ranges::iota` to the `ranges_robust_against_*` right? Or should it be added to the `robust_against_*` tests?

https://github.com/llvm/llvm-project/pull/68494