fix: HPB partial updates no longer drop the call when a participant joins

[alauzon]

Fixes #5452

Problem

With external signaling (HPB), onParticipantsUpdate delivers partial updates containing only changed participants. The previous code treated both onUsersInRoom (full list) and onParticipantsUpdate (partial update) identically: any participant absent from the list was moved to the left collection.

When a new participant joined via HPB, the local user was not included in the partial update (because the local user didn't change). This caused the local participant to appear in left, which made CallActivity.handleCallParticipantsChanged conclude:

isSelfInCall = false
// → "Most probably a moderator ended the call for all."
hangup(shutDownView = true, endCallForAll = false)

The call was dropped by the Android client as soon as another participant joined.

Fix

processParticipantList now takes a boolean fullList parameter:

• onUsersInRoom passes fullList=true — absent participants have left (original behaviour)
• onParticipantsUpdate passes fullList=false — absent participants are still in the call and are moved to unchanged instead of left

handleCallParticipantsChanged builds participantsInCall from joined + updated + unchanged, so the local user stays present, isSelfInCall remains true, and the call is not dropped.

[mahibi]

thank you @alauzon we will have a closer look soon

[mahibi]

Please excuse the current delays in pull request reviews.
The PR is on our list.

[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.)