HelperText as a generic component

[Pierstoval]

This feature is spread across several other components, and I had to use it on a custom project at some point, and I thought it would be a better option to be able to reuse the base Carbon feature directly as a Svelte component.

I ran yarn build:docs and it seems fine, and I updated all components using it so the behavior shouldn't change, since the HTML code behind is the same as before, so there is no breaking change.
I also ran yarn lint, and it updated some other files, sorry for that 😅.

I have questions though:

• I'm still not sure about whether the helperText parameter should be flexible and injected either as an argument or as a <slot> element, but IMO having both available is fine, please tell me if it's ok.
• Another thing I'm not 100% sure for now is the name: HelperText seems generic, but it's mostly used in Form components. Carbon design system initially shows this behavior only in forms. Should I therefore put it in the Form namespace? Rename it FormHelperText? Something else?

Side-note: The initial reason for this was that at some point I noticed that some form components didn't have the helperText feature (like Checkbox for instance). So if this is merged, I think it's going to be a bit simpler to add support for helperText to many other components 👌