[Docs] Avatar family migration documentation (7 components)

[georgewrmarshall]

Summary

Add migration documentation for the Avatar component family (7 components) that have been migrated from Extension/Mobile to MMDS.

Components

• AvatarBase
• AvatarIcon
• AvatarAccount
• AvatarNetwork
• AvatarToken
• AvatarFavicon
• AvatarGroup

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

Include:

• Breaking changes between Extension/Mobile and MMDS
• Prop mapping tables
• 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/avatar*
• Mobile: app/component-library/components/Avatar*

Example Reference

Text component migration: https://github.com/MetaMask/metamask-design-system/blob/main/packages/design-system-react/MIGRATION.md#text-component

Labels

documentation