Honor whitespace escape sequences in `yank-join` about helix HOT 4 OPEN

fn escape(separator: &str) -> Cow<'_, str> {
    enum State {
        Normal,
        Escape,
    }

    let mut escaped = String::new();
    let mut state = State::Normal;
    let mut is_escaped = false;

    for (idx, ch) in separator.char_indices() {
        match state {
            State::Normal => match ch {
                '\\' => {
                    if !is_escaped {
                        // PERF: As not every separator will be escaped, we use `String::new` as that has no initial
                        // allocation. If an escape is found, then we reserve capacity thats the len of the separator
                        // as the new escaped string will be at least that long.
                        escaped.reserve(separator.len());
                        if idx > 0 {
                            // First time finding an escape, so all prior chars can be added to the new escaped version
                            // if its not the very first char found.
                            escaped.push_str(&separator[0..idx]);
                        }
                    }
                    state = State::Escape;
                    is_escaped = true;
                }
                _ => {
                    if is_escaped {
                        escaped.push(ch);
                    }
                }
            },
            State::Escape => match ch {
                'n' => {
                    escaped.push('\n');
                    state = State::Normal;
                }
                't' => {
                    escaped.push('\t');
                    state = State::Normal;
                }
                'r' => {
                    escaped.push('\r');
                    state = State::Normal;
                }
                '\\' => {
                    escaped.push('\\');
                    state = State::Normal;
                }
                _ => {
                    escaped.push('\\');
                    escaped.push(ch);
                    state = State::Normal;
                }
            },
        }
    }

    if is_escaped {
        escaped.into()
    } else {
        separator.into()
    }
}