Function unescape_non_raw_common

fn unescape_non_raw_common<F, T: From<char> + From<u8>>(
    src: &str,
    mode: Mode,
    callback: &mut F,
)
where
    F: FnMut(Range<usize>, Result<T, EscapeError>),

Takes a contents of a string literal (without quotes) and produces a sequence of escaped characters or errors.