[9.x] Restore v8 behaviour of base query for relations

[tpetry]

As commented on #41918 I found a new inconsistency in the Laravel 8.x and 9.x implementation with the fix by @driesvints.

In Laravel v8 the implementation for getBaseQuery was:

public function getBaseQuery()
{
    return $this->query->getQuery();
}

With the recently merged fix it's now the following which is different (it's now applying the scope!):

public function getBaseQuery()
{
    return $this->toBase();
}

public function toBase()
{
    return $this->query->applyScopes()->getQuery();
}

I restored the exact behavior of Laravel 8.x that getBaseQuery and toBase are both operating directly on the Eloquent\Builder object. So any change in Eloquent\Builder::toBase() is also automatically reflected on Relationship::toBase() as in Laravel 8.x.

[driesvints]

This probably indeed is the better fix. Thanks @tpetry.