[libcxx-commits] [libcxx] [libc++][mdspan] Fix `mdspan::operator[]` bounds checking and implement LWG4020 (PR #192269)

[A. Jiang via libcxx-commits]

frederick-vs-ja wrote:

@eiytoq I replaced the Godbolt link with the actual example which is possibly more suitable for squashed commit message, IMO. Please double-check.

https://github.com/llvm/llvm-project/pull/192269