Automatically triggering effects from emoji use is unexpected and disruptive

### Description

The recent addition of effects triggered by emoji https://github.com/vector-im/element-web/issues/14676 is very surprising to me as it's not clear that it will be triggered at all. I use the 🎉 emoji frequently and it's not my intention when writing a message to my colleagues that the inclusion of this single character will result in them being confronted with a full screen effect.

The deliberate slash commands seem fine as that's a conscious action by the sender. I'm aware of the setting to turn these off but that only affects me (I think) and not my recipients.

### Steps to reproduce

- Send a message like "Passing CFF tests 🎉" in a group channel
- Witness an unwanted full screen confetti effect

Describe how what happens differs from what you expected.

When I'm sending a message I expect that message to be delivered as I typed it. It is very surprising that by using a particular character I might trigger a full screen visual effect for my recipients.

### Version information

- **Platform**: web (in-browser)

For the web app:

- **Browser**: Firefox 84.0.2
- **OS**: Arch Linux
- **URL**: Private server on *.element.io, version: v1.7.16; olm version: 3.2.1