[llvm] [ADT] Teach StringRef to take basic features from std::string_view (NFC) (PR #113797)

[David Blaikie via llvm-commits]

dwblaikie wrote:

> Seems that there is no conclusion on the approach. #113775 is reverted https://discourse.llvm.org/t/migrating-llvm-stringref-to-std-string-view/82785

As mentioned in that thread, I think it's still good to converge the APIs, even if they never get deduplicated.

https://github.com/llvm/llvm-project/pull/113797