Computed keys

[Naddiseo]

TODO: Does our syntax cover computed keys?

let o = {
    [ key ] TypeHint : thing, // like this?
};

[Naddiseo]

Verified, it does:
PropertyDefinition : PropertyName TypeHint : AssignmentExpression
PropertyName expands to
PropertyDefinition : ComputedPropertyName TypeHint : AssignmentExpression
ComputedPropertyName expands to
PropertyDefinition : [ AssignmentExpression ] TypeHint : AssignmentExpression

TODO: Does the key need hinting? I think typescript allows hint inside the key.