Restore _convert_item_to_dict Functionality in ItemValidationPipeline for Compatibility

[arslansherazi]

This pull request restores the _convert_item_to_dict functionality in the ItemValidationPipeline, which was available in previous versions but removed in the current release.

For users who extended the ItemValidationPipeline with the spidermen pipeline and relied on the _convert_item_to_dict function, this removal could break their code. By reintroducing this functionality, we ensure those users can continue using it without needing to refactor their pipelines.

This update provides compatibility for users relying on the older version's behavior, while allowing users of the current version to avoid any issues or breaking changes.

Sample Code: