Improve tuple errors

[danquirk]

var [x, y] = [1];

The error is on y saying 'Type [number] has no property 1' which is not the most intuitive result. The more human readable explanation would be a span on either the full LHS or full RHS saying 'Tuple type [number] with length 1 cannot be assigned to a tuple type with length 2.'

Another:

var [x, [a,b]] = [[]];

The error is on the inner binding pattern [a,b] saying 'Type [undefined[]] has no property 1'. Again it would be much more understandable to error on the entire LHS or RHS saying 'Tuple type [undefined[]] with length 1 cannot be assigned to tuple type with length 2.'