fix(types): export file upload types

[johnnaegle]

Description

Export types FileUpload and FilesUpload.

If you are using typescript, these two types are needed to properly
type the callbacks: onFileSelect, onDialogClose

// These types currently aren't exported
import type { FileUpload, FilesUpload } from '@uploadcare/react-widget';
import { Widget } from '@uploadcare/react-widget';

// So you can't type these callbacks
const  onFileSelect = (fileInfo: FileUpload | FilesUpload | null):void => {
  ...
};
const  onDialogClose = (fileInfo: FileUpload | FilesUpload | null):void => {
  ...
};

<Widget
  onFileSelect={onFileSelect}
  onDialogClose={onDialogClose}
 ... 
/>

Checklist

• Tests (if applicable)
• Documentation (if applicable)
• Changelog stub (or use conventional commit messages)

[johnnaegle]

I have some more TS changes that I'm still working through:
master...johnnaegle:master

I can make a new PR with all those changes if they look OK. Reverse engineering the types hasn't been easy, but what I've got so far works with the client we've already built. I could very well have missed something

[johnnaegle]

#253 has more type corrections than this PR

[nd0ut]

Hey @johnnaegle
Many thanks for contribution. Collection/group types looks OK, make a new PR please.