Add icon preview to Admin UI Extensions documentation

[davebcn87]

What does this PR do?

Adds an interactive icon preview component to the Icon documentation page for Admin UI Extensions. This allows developers to browse and search through all available icons in the Shopify Admin design system.

Features

• Interactive icon browser: Visual preview of all 500+ available icons
• Search functionality: Quickly find icons by name with real-time filtering
• Pagination: Navigate through icons in organized pages (10 icons per page)
• Auto-generated icon list: Automatically stays in sync with the TypeScript definitions, ensuring the documentation always shows the current set of available icons
• Clean layout: Icons displayed in a 2-column grid with their names for easy reference

Why is this needed?

Developers building Admin UI Extensions need to know which icons are available for use in their applications. This visual browser makes it easy to:

• Discover available icons without checking the source code
• Search for specific icons by name
• See exactly how each icon looks
• Copy the exact icon name for use in their code

Testing

• Icon preview displays correctly with all 513 current icons
• Search filters icons in real-time
• Pagination works for navigating through large icon sets
• Documentation builds successfully with auto-generated icon list

[github-actions]

We detected some changes in packages/*/package.json or packages/*/src, and there are no updates in the .changeset directory. If the changes are user-facing and should cause a version bump, run yarn changeset to track your changes and include them in the next release CHANGELOG. If you are making simple updates to repo configuration, examples, or documentation, you do not need to add a changeset.

[jplhomer]

🚀 I love it