[diff.cpp14.library] missing Annex C note for new C++17 headers

[timsong-cpp]

[diff.cpp03.library] has a note for new headers added in C++11, and [diff.cpp11.library] has a note for the one new header added in C++14. We do not appear to have a similar note for the headers added in C++17 <any>, <optional>, <variant>, <filesystem>, <execution>, <memory_resource>, maybe <charconv> (or should that be handled as C++20)?

[zygoloid]

If you put together a pull request for this, I would take it as an editorial change to C++17.