Sliding sync expects all state events to be in `required_state`. State
events in `timeline` **must be ignored**. However, in sync v2, state
events in `timeline` **must be handled**.
In the sync response flow, both sliding sync and sync v2 uses the same
`handle_timeline` method. This patch adds an argument to ignore state
events. This is not ideal, but it's a temporary solution as a first
step. The next step is to refactor this code, but let's start easy.
The rest of the patch updates the tests accordingly.
Ivan Enderlin
72dc307400