Function quoted_string

fn quoted_string<I, E>(input: I) -> IResult<I, I, E>
where
    I: Input + Offset,
    <I as Input>::Item: AsChar,
    E: ParseError<I>,

QUOTED-STRING = DQUOTE *( qdtext / quoted-pair ) DQUOTE

If the parser succeeds, we return the unmodified string (with backslashes included) to prevent allocation and to make sure that all of the return types are consistent when using nom combinators