[TypeDeclaration] Skip anonymous class return in NarrowObjectReturnTypeRector

[TomasVotruba]

Fixes narrowing a method return type to an anonymous class name.

When a method returns $this from inside an anonymous class, the rule narrowed the return type to the generated anonymous class name (e.g. \AnonymousClass62d65...), producing invalid, non-referenceable code.

private function createEmail(): Email
{
    return new class extends Email {
        public function setId(int $id): Email
        {
            $this->id = $id;

            return $this; // was narrowed to \AnonymousClass...
        }
    };
}

Now anonymous classes are skipped, keeping the original (correct) Email type.