feat: adding button icon to design system react

[georgewrmarshall]

Description

This PR adds ButtonIcon component to the design system react.

Key features include:

1. Three size variants (sm, md, lg)
2. Support for floating/contained style
3. Inverse color mode for dark backgrounds
4. Built-in accessibility with required aria labels
5. Comprehensive test coverage
6. Full Storybook documentation

The component is built on top of our existing ButtonBase component and integrates with our Icon system.

Related issues

Fixes: #387

Manual testing steps

1. Run Storybook (yarn storybook)
2. Navigate to React Components/ButtonIcon
3. Test different configurations:
   • Try all size variants (sm, md, lg)
   • Toggle floating mode
   • Toggle inverse mode on dark background
   • Verify disabled state
   • Check hover and active states
   • Check controls
   • Check accessibility tests

Screenshots/Recordings

Before

N/A - New component

After

after720.mov

Pre-merge author checklist

• I've followed MetaMask Contributor Docs
• I've completed the PR template to the best of my ability
• I've included tests (100% coverage for ButtonIcon component)
• I've documented my code using JSDoc format
• I've applied the right labels on the PR

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.