[Improvement]: Rename `__getRawRelationData()`

[solverat]

Improvement description

PHP reserves __ for magic methods, and static analysis tools (PHPStan, PhpStorm) correctly flag these as violations.

Proposed Solution

  /** @internal */
  public function getDataObjectRawRelationData(): array {}

  /** @internal */
  protected ?array $dataObjectRawRelationData = null;

The blocked vars reference in Concrete.php must be updated accordingly

https://github.com/search?q=repo%3Aopen-dxp%2Fopendxp+%22__rawRelationData%22&type=code