impl LowerHex, UpperHex for `&[u8]`

[luser]

I've found myself writing some version of bytes_to_hex more than once, and it looks like I'm not the only one:
https://github.com/search?l=Rust&q=bytes_to_hex&type=Code&utf8=%E2%9C%93

I think a nice addition would be to impl LowerHex and UpperHex for &[u8], so that you could simply do format!("{:x}", bytes).

[ollie27]

Dupe of #33127, rust-lang/rfcs#1916.

[luser]

Thanks, should have looked harder!