[clang-tools-extra] [clang-tidy] Add readability-use-span-first-last check (PR #118074)

[via cfe-commits]

pkasting wrote:

FWIW I agree that `last(size() - n)` is worse than `subspan(n)`, and that the reverse transform (`subspan(size() - n)` -> `last(n)`) is better.

https://github.com/llvm/llvm-project/pull/118074