Should provide object member completions when missing commas; also should insert missing commas

[DanielRosenwasser]

Today, if you try to request completions after an object literal element that has no comma, you'll get no useful contextual completions.

interface ColorPalette {
    primary?: string;
    secondary?: string;
}

let colors: ColorPalette = {
    primary: "red"
    /*$*/
};

interface ColorPalette {
    primary?: string;
    secondary?: string;
}

let colors: ColorPalette = {
    primary: "red"
    seconda/*$*/
};

My proposal is that we do something similar to what we do in class elements, but maybe a little smarter.

We should continue to provide contextual completions, and also, those completions should automatically insert the , on the previous line.