[11.x] feat: add better closure typing in QueriesRelationships

[calebdw]

Hello!

This adds better closure types to the methods in QueriesRelationships:

$query->whereHas($user->posts(), function ($query) {
    // Knows that it's a Post Builder!
    assertType('Illuminate\Database\Eloquent\Builder<Illuminate\Types\Builder\Post>', $query);
});
$query->whereHasMorph($post->taggable(), 'taggable', function ($query, $type) {
    // Knows the parameter types!
    assertType('Illuminate\Database\Eloquent\Builder<Illuminate\Database\Eloquent\Model>', $query);
    assertType('string', $type);
});

Closes calebdw/larastan#25

Thanks!