Typescript: SpreadAssignment support

[OlafConijn]

Spread assignments are not supported:

const y = {a: 1, b: 2};
const x = { ... y, c: 3};

a workaround is to explicitly copy over each property:

const y = {a: 1, b: 2};
const x = {a: y.a, b: y.b, c:3};