[Docs] Button, ButtonBase, Checkbox, TextButton migration documentation

## Summary

Add migration documentation for Button-related components and form components that have been migrated from Extension to MMDS.

## Components

- Button
- ButtonBase
- Checkbox
- TextButton

Note: ButtonPrimary, ButtonSecondary, ButtonLink are variants of Button and covered by the same migration docs.

## Definition of Done

### 1. MIGRATION.md Sections
Add migration sections with API maps to:
- `packages/design-system-react/MIGRATION.md`
- `packages/design-system-react-native/MIGRATION.md` (if applicable)

Include:
- Breaking changes between Extension/Mobile and MMDS
- Prop mapping tables (size, variant enums, etc.)
- Before/after code examples

### 2. README Links
Add migration section to each component's README.mdx:
- Link to relevant MIGRATION.md section

### 3. @deprecated Updates
Add migration links to JSDoc in:
- Extension: `ui/components/component-library/button*`, `checkbox*`, `text-button*`
- Mobile: Check if similar components exist

## Example Reference
ButtonIcon version migration: https://github.com/MetaMask/metamask-design-system/blob/main/packages/design-system-react/MIGRATION.md#buttonicon-variant-prop

## Labels
documentation

Start with the ButtonIcon migration section in packages/design-system-react/MIGRATION.md, then inspect the corresponding MIGRATION.md files, component README.mdx files, and Extension/Mobile component paths named in the issue. Document Button, ButtonBase, Checkbox, and TextButton migration mappings, examples, README links, and @deprecated links, then verify that each requested component is covered in the relevant React and React Native documentation.

Written by the indexing model from the issue text.