Allow array literal form to follow spread operator in function call args. Fixes gh-2060

IIRC (this is from memory, might be slightly wrong) it's really any assignment expression (aka `AssignmentExpression :: ... AssignmentExpression`) --- so basically if there's a `...` it's going to be fine. It could be `(new Map).set('a', 1).set('b', 2)` and it would still be spreadable