Generate docblocks: Class not imported if nested

[dantleech]

Currently there is a bit of a mess when we do:

foreach ($type->classLikeTypes() as $type) {
    $builder->use($type->__toString());
}

as it does not include nested types, e.g. Iterator<int, Foobar>, Foobar will not be included in the set of "class like types".

It is not exactly clear what classLikeTypes means -- it is currently used in completion (e.g. all types that can be completed in a union or interesction type) and in the above case, but clearly they are different things.

[dantleech]

Fixed