Add u8::escape_default and [u8]::escape_default

[camelid]

The standard library has several functions for printing escaped text:

• char::escape_default for printing escaped Unicode characters
• str::escape_default for printing escaped Unicode strings
• std::ascii::escape_default for printing escaped ASCII bytes

I propose that we add associated functions to u8 and [u8] that are like
{char,str}::escape_default but for ASCII. The std::ascii::escape_default
function is not very discoverable – I was expecting a u8::escape_default
function like for char – and in fact I was about to post a question on
Stack Overflow when I found it in the std docs and posted an answer to
help others who also don't realize the existence of std::ascii::escape_default.

[m-ou-se]

This sounds like #77174

[camelid]

Yep, I'll close this. Thanks!