docs(S2): fix icon import clipboard content to add underscore for icons starting with number

[reidbarber]

Import statement for icons like 3DAsset were being copied like:

import 3DAsset from '@react-spectrum/s2/icons/3DAsset';

which is invalid. It should be:

import _3DAsset from '@react-spectrum/s2/icons/3DAsset';

Same for the illustrations.

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue.
• Added/updated unit tests and storybook for this change (for new code or code which already has tests).
• Filled out test instructions.
• Updated documentation (if it already exists for this component).
• Looked at the Accessibility Practices for this feature - Aria Practices

📝 Test Instructions:

Try copying 3DAsset's import in the icons search, and the illustrations search.

🧢 Your Project:

[rspbot]

Build successful! 🎉

• View the storybook
• View the S2 storybook
• View the S2 docs
• View the React Aria docs

[rspbot]

Build successful! 🎉

• View the storybook
• View the S2 storybook
• View the S2 docs
• View the React Aria docs

[rspbot]

Build successful! 🎉

• View the storybook
• View the S2 storybook
• View the S2 docs
• View the React Aria docs