Previous discussion about removing several selected groups only delete one of them #8390

Thank you LIM0000 for your PR.
Indeed, this solves the issue for Remove groups > Also remove subgroups.
However, a similar issue remains for Remove groups > Keep subgroups.
Please, could you look at this closely-related issue?

Proposed solution:

Fixes #8390

• When removeGroupKeepSubgroups() is called, iterate through all selected groups instead of the group that triggers the event handler.
• Popup a confirmation dialog and confirm if user decides to delete:
  • single group
  • multiple groups (if multiple groups selection)
• All subgroups are assigned to their corresponding grandparents if there are any. Otherwise, they are assigned to All entries.

Single group deletion

Multiple groups deletion

• Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• 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.