Permit batches of events to be collapsed by default, when events are visible.

### Your use case

#### What would you like to do?

When I have enabled the ability to view events in a chat, I do not generally want to see them all the time; rather, I want to know when events are present, such that I can expand them when need be.

#### Why would you like to do it?

It would mean that I would not need to re-enable the preference whenever I want to see events, and would be able to focus upon actual content when event observation is enabled.

#### How would you like to achieve it?

ASAP, insofar as is feasible and reasonable.

### Have you considered any alternatives?

Events can already be disabled in client preferences.

The issue does not name any implementation files, tests, or entry points. Start by locating the Element client UI and preference handling for visible events, then determine how event batches are currently rendered and what existing client behavior should be preserved. Done means visible events are collapsed by default while users can expand them without disabling event visibility.

Written by the indexing model from the issue text.