fix(Button): remove support for className

[stephenjwatkins]

📝 Changes

• remove support for overwriting className on Button

<Button className="extend" /> overwrites button styles by accidentally spreading props at the end. this is a pretty big departure from Easy UI's current expectations that presentational components contain their styles and provide extensions only through props, and can cause further breaking changes later with a harder upgrade path

🚨 this is technically a breaking change but due to being in pre-release mode, it's better served as a patch. we will need to update 4 instances in our products. these can be found with this <Button([\s\n\r]+|[^>]+)className regex 🚨

✅ Checklist

Easy UI has certain UX standards that must be met. In general, non-trivial changes should meet the following criteria:

• Visuals match Design Specs in Figma
• Stories accompany any component changes
• Code is in accordance with our style guide
• Design tokens are utilized
• Unit tests accompany any component changes
• TSDoc is written for any API surface area
• Specs are up-to-date
• Console is free from warnings
• No accessibility violations are reported
• Cross-browser check is performed (Chrome, Safari, Firefox)
• Changeset is added

Strikethrough any items that are not applicable to this pull request.