[Feature]: Custom Styles for Selected Text in Input Text Fields
### What's the feature?

I was using the tldraw extension in VS Code and found it to be an awesome tool! However, I would like to suggest a new feature.

Currently, when I add text and apply styles (e.g., bold, italic, underline), the styles are applied to the entire text. It would be great if we could apply custom styles to only a selected portion of the text while keeping the rest of the text unchanged.

### Example
1. Add a text field.
2. Type "Hello World".
3. Select only "World" and apply a custom style (e.g., bold or a different color).
4. The result: "Hello **World**" or "Hello *World*".

This would allow for more flexibility and finer control over text formatting within the extension.

### Where would you like this feature?

The developer package

### Contact Details

_No response_

### Code of Conduct

- [X] I agree to follow this project's Code of Conduct