Allow a rest pattern before closing brace when destructuring

Example for a struct:

let Self {
    x,
    y,
.. } = self;

match x {
    Variant::A {
        a,
        b,
    .. } => { /* snip */ }
    _ => todo!(),
}

Currently a .. is placed either on a separate line, or, in case of match and/or a short list of required fields, right after the trailing comma, all on the same line. I also think the above style may serve the best for the same purpose that a trailing commas are intended for. Please consider, thanks.

Start by reproducing the struct and match examples from the issue with rustfmt, then locate the existing formatting behavior for destructuring rest patterns. Done means rustfmt consistently permits and preserves the shown placement of .. before the closing brace without regressing other destructuring formats.