fix(systemtags): Dispatch events when bulk assigning system tags

[rolandinus]

Summary

The setObjectIdsForTag method is missing event dispatching. This prevents apps from reacting
to tag changes when using the bulk tag assignment feature which was added with Nextcloud 31.
This creates a different beheaviour to when tags are assigend via the sidebar, where the assignTags and unassignTags methods are used which do dispatch the events.

This fix:

• Calculates which objects are removed and which are added
• Dispatches MapperEvent::EVENT_UNASSIGN for removed objects
• Dispatches MapperEvent::EVENT_ASSIGN for added objects

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[provokateurin]

LGTM, but didn't test.

[skjnldsv]

same, code looks good

[skjnldsv]

/backport to stable31

[welcome]

Thanks for your first pull request and welcome to the community! Feel free to keep them coming! If you are looking for issues to tackle then have a look at this selection: https://github.com/nextcloud/server/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22

[github-actions]

Hello there,
Thank you so much for taking the time and effort to create a pull request to our Nextcloud project.

We hope that the review process is going smooth and is helpful for you. We want to ensure your pull request is reviewed to your satisfaction. If you have a moment, our community management team would very much appreciate your feedback on your experience with this PR review process.

Your feedback is valuable to us as we continuously strive to improve our community developer experience. Please take a moment to complete our short survey by clicking on the following link: https://cloud.nextcloud.com/apps/forms/s/i9Ago4EQRZ7TWxjfmeEpPkf6

Thank you for contributing to Nextcloud and we hope to hear from you soon!

(If you believe you should not receive this message, you can add yourself to the blocklist.)