[7.x] Allow to use alias of morphed model

[thewebartisan7]

At the moment if you use hasMorph() you need to use model class name and can't use alias, you need to use Relation::getMorphedModel.
But this is already done when you use * which auto discover morphed relations.

Moving this conversion for all case allow to use directly aliases.

Example now:

        $morphable =  [
                "App\AnotherModel",
                Relation::getMorphedModel('alias')
        ];
        $dataset = MyModel::query()
            ->whereHasMorph('morphable', $morphable)
            ->with('morphable')
            ->orderBy('id')
            ->limit(50)
            ->get()
            ->groupBy('morphable_type');

With this change can be:

        $morphable =  [
                "App\AnotherModel",
                'alias',
                'another',
                "App\YetAnotherModel",
        ];
        $dataset = MyModel::query()
            ->whereHasMorph('morphable', $morphable)
            ->with('morphable')
            ->orderBy('id')
            ->limit(50)
            ->get()
            ->groupBy('morphable_type');