Support an object destructuring assignment with for-in.

[Kray-G]

Support like the following syntax.

var elems = [
    { a: 1, b: 2, c: 3},
    { a: 10, b: 20, c: 30},
    { a: 100, b: 200, c: 300},
];

for (var { a, b, c } in elems) {
    System.println([a, b, c]);
}

Here is the expected result.

[1, 2, 3]
[10, 20, 30]
[100, 200, 300]