[Story] Render heroes avatar when a room has no avatar

[bmarty]

Description

• As a user I want to see avatar of heroes when a room does not have avatar so that it can give more information to distinguish rooms.

Acceptance criteria

• Avatar for rooms with 1, 2, 3 and 4 heroes are correctly rendered:
  • in the room list
  • in the room timeline header
  • in the room detail screen

Design: https://www.figma.com/design/G1xy0HDZKJf5TCRFmKb5d5/Compound-Android-Components?node-id=1474-886&t=Aw5gIQI0PSBCqERx-1

Note: implementation has been started on Android in https://github.com/element-hq/element-x-android/pull/3058, so it's just a matter of removing some code (elementHeroes) and maybe iterate on design for the case 2 heroes (to be confirmed with @amshakal)

Current rendering on Android, for the case 2, 3 an d4 heroes:

A is the first hero, B the second, C the third and D the fourth.

Other Android screenshots:

Leads

• Tech: @bmarty
• Design: @amshakal

Size estimate

M

Dependencies

• None

Out of scope

• Nothing

Open questions

### Questions

Subtasks

### Android

### iOS

### Rust

### Other

Sign-off

Android

• [ ] Design sign-off on completion
• [ ] QA sign-off on completion
• [ ] Product sign-off on completion

iOS

• [ ] Design sign-off on completion
• [ ] QA sign-off on completion
• [ ] Product sign-off on completion