Room ordering: Make unit tests to ensure that there is no regressions

Make unit tests to test every cases that can impact room list ordering.

Some example:
* Someone left the room
* Someone invites you
* without message
* with a message
* Someone change is avatar
* Topic is changed
* And so on

The issue names no files or existing tests. Start by locating the room-list ordering implementation and related unit tests in the iOS project, then run the relevant test target. Done means the listed room events, including invites with and without messages, are covered by tests that detect ordering regressions.

Written by the indexing model from the issue text.