Automatically convert emoji shortcodes to emojis

### Your use case

#### What would you like to do?
I would like to type emoji shortcodes and have Element automatically convert my shortcode into an emoji, even if I didn't click on one in the selector

#### Why would you like to do it?
I am used to typing emoji shortcodes directly in the text bar

#### How would you like to achieve it?
To me, there 2 parts in this issue:
- The emoji selector invoked from the shortcode should be quicker to quick in (right in, it seems like there's a 0.5 delay or so when starting to type an emoji)
- When finishing the emoji by entering the second `:`, the shortcode should be converted into an emoji automatically (e.g. by typing `:x:`)

This feature request focuses on the second point
Example of these features: Discord

### Have you considered any alternatives?

_No response_

### Additional context

Behaviours in Element, and in Discord

https://github.com/user-attachments/assets/d12d624b-aea6-4111-b826-ae27a3715639
https://github.com/user-attachments/assets/015b0eda-f31b-4053-bd51-29b36530a4ec

I am ready to submit a PR for this, if you agree with the feature request