Animated emojis rain down when the trigger is off the page

### Steps to reproduce

1. Someone posts :tada: and then a bunch more messages
2. Wait until :tada: is not visible any more

### Outcome

#### What did you expect?
Animations stop raining down as soon as :tada: is off the screen

#### What happened instead?
I keep seeing animations even though :tada: is probably two screens away from latest message

### Operating system

_No response_

### Browser information

Chromium 96.0.4664.110 (Official Build) Arch Linux (64-bit)

### URL for webapp

develop.element.io

### Application version

Element version: cfa97212f73e-react-074fec359b9f-js-7d2a5afa6dc9 Olm version: 3.2.8

### Homeserver

_No response_

### Will you send logs?

No

Start by reproducing the issue in the Element webapp with an animated emoji followed by enough messages to move it off-screen. Trace the frontend code that starts and stops emoji animations based on message visibility; done means animations stop when the triggering emoji leaves the visible area, with the behavior verified in the affected Chromium setup.

Written by the indexing model from the issue text.