An element is fillable if its:
- In dom
- Not display:none or visibility:hidden
- textarea or input or contenteditable
if textarea or input it must also be
- not readOnly
- not disabled
#133
This makes it so that JSHandles and ElementHandles are aware of what types they point to. As a fun bonus, `$eval('input')` knows its going to get an HTMLInputElement.
Most of this patch is casting things where previously we just assumed ElementHandles held the right kind of node. This gets us closer to being able to turn on `noImplicityAny` as well.
#6
