Fix whereIn subquery for Laravel 5.8+

[szainmehdi]

The way Laravel handles subqueries in the whereIn() method has changed in Laravel 5.8. (before, after). When using this library, any query bindings in the subquery within a whereIn clause were discarded, resulting in SQL errors.

For example:

// Terrible example query but hopefully, it gets the point across.
$query = Product::query()->where('type', 'physical')->whereIn('id', function ($sub) {
    $sub->select('product_id')->from('orders')->where('total', '>',  25.00);
});


dd($query->toSql(), $query->getBindings());

// Before this fix, in Laravel 5.8+
// select * from "products" where "type" = ? and "id" in (select "product_id" from "orders" where "total" > ?)
// [0 => 'physical']

// After this fix, in Laravel 5.8+
// [0 => 'physical', 1 => 25.00]

Before, when a query with a whereIn clause with a subquery was performed, the $where['type'] would be set to InSub or NotInSub depending on the operator, in which case our custom whereIn method would basically do nothing and return early.

laravel-mutate/src/Database/EloquentBuilder.php

Lines 96 to 100 in b96b860

	if ($where['type'] === 'InSub' || $where['type'] === 'NotInSub') {
	$this->query->wheres[] = $where;
	return parent::whereIn($column, $values, $boolean, $not);
	}

Sidenote: we shouldn't be calling parent::whereIn() again here since we've already called it in the lines above. This has also been corrected in this PR.

Now, with the changes in Laravel 5.8+, the check we were performing no longer applies. The $where['type'] is always either In or NotIn. Instead of checking the value of $where['type'], we can just check to see if it's "queryable" using the same logic that the Illuminate\Database\Query\Builder class uses, and return early like before.