Make it possible to keep leave rooms when syncfilter includes them

[krille-chan]

Preflight Checklist

• I could not find a solution in the existing issues, docs, nor discussions

Describe your problem

Right now we are using the leaveRoom in the sync as a trigger to wipe everything from memory and from database. But if we set a SyncFilter to keep left rooms we should handle them like normal rooms.

Describe your ideal solution

This needs some changes in our handleSync logic. To check if we wanna do this, we could check: Client.syncFilter.room?.includeLeave

Version

0.38.0

Security requirements

No response

Additional Context

No response