Closes #12561

ViewModelListCellFactory.java contained the calls to the OnDrag() properties like onDragOver() and onDragDrop(), which were necessary for the drag and drop functionality. We added an event.consume() call and a call to the parent to restart the indicator for the drag and drop file indicator. This allowed us to repeatedly drag and drop files in the correct cell.

Now works

Mandatory checks

• I own the copyright of the code submitted and I license it under the MIT license
• Change in CHANGELOG.md described in a way that is understandable for the average user (if change is visible to the user)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (if change is visible to the user)
• Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.