Refactor EventTile using the MVVM pattern - #5a

[rbondesson]

Checklist

• I have read through review guidelines and CONTRIBUTING.md.
• Tests written for new code (and old code if feasible).
• New or updated public/exported symbols have accurate TSDoc documentation.
• Linter and other CI checks pass.
• I have licensed the changes to Element by completing the Contributor License Agreement (CLA)

Refactor EventTile using the MVVM pattern

Partially implements: https://github.com/element-hq/wat-internal/issues/414

Summary - Step 5a

Extract feature-specific EventTile state into focused view-model helpers
(a follow up PR will contain extraction of E2E padlock state)

Changes

• Extract receipt state
• Extract thread state
• Extract reaction relation state
• Extract reply-chain state
• Added focused view-model tests for each extracted state helper

Implementation plan

1. Cover existing behavior with tests - Refactor EventTile using the MVVM pattern - #1 #33463
   Add/maintain focused tests around current EventTile behavior before moving logic.

2. Extract pure decision helpers - Refactor EventTile using the MVVM pattern - #2 #33489
   Move low-risk derived state calculations out of EventTile, without changing rendering ownership yet.

3. Introduce small view models - Refactor EventTile using the MVVM pattern - #3 #33516
   Start with isolated surfaces such as timestamp visibility, root attributes/classes, message type classes, and sender/avatar decisions.

4. Move interaction state - Refactor EventTile using the MVVM pattern - #4 #33539
   Extract hover/focus/action-bar/context-menu state once the pure rendering decisions are stable.

5. Move feature-specific state
   Extract reaction relations, reply-chain state, thread-info state, and receipt state into separate view-model boundaries.

6. Thin the React component
   Keep EventTile mostly as composition/wiring: render views, pass event handlers, and bridge Matrix/React context.

7. Split view components
   Move stable UI fragments into smaller view components where it reduces EventTile complexity.

8. Remove legacy duplication
   After behavior is covered by view models and views, clean up old inline helpers and dead conditional branches.