Custom Stickers & Emoticons (MSC2545) like it works in Cinny or FluffyChat

### Your use case

#### What would you like to do?

I would like to see native stickers and custom emoticons support in Element, like it works in Cinny or FluffyChat.


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

Clients like Cinny already using native sticker packs instead of integrations in Element. It's work faster and have simplified manage process.

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

Cinny using [this specs](https://github.com/Sorunome/matrix-doc/blob/soru/emotes/proposals/2545-emotes.md), and it's work perfectly. I also write a [small tool](https://github.com/foresle/matrix_stickers_manager) to manage sticker packs. Need to just copy logic to Element :)

I can't write code for this for itself that I don't know Kotlin, but think it's a very important feature, so I created this issue.

### Have you considered any alternatives?

_No response_

### Additional context

_No response_

### Are you willing to provide a PR?

No