Give a helpful error when trying to relate primitives to the boxed/apparent backing types.

``` ts
var x = new Number();
var y = 100;
y = x;
```

Current error: `Type 'Number' is not assignable to type 'number'.`
Suggestion:

```
Type 'Number' is not assignable to type 'number'.
  'number' is a primitive type while 'Number' is a boxed object. Prefer using 'number' when possible.
```
