Allow "final" modifier when importing a method from a trait 

### Description

Not sure why this is not allowed currently, but it'd be nice allowing it if there aren't any blockers:

```php
trait SomeTrait {
    function someMethod() {}
}

class SomeClass {
    use SomeTrait {
        someMethod as final;
    }
}
```

This currently produces: "Cannot use 'final' as method modifier"