Stabilize `str::from_utf8_unchecked` as `const`
Stabilize `str::from_utf8_unchecked` as `const`

graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust