fix: textfield prefix design feedback

[snowystinger]

Closes

Design feedback that space between small prefix, such as the first example in the textfield docs, was too large. It was leftover from when I thought the prefix was only going to be wf icons or text.

✅ 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:

Go to docs, there shouldn't be a large amount of space between the '#' and the placeholder in the first example of Textfield's prefix example.

🧢 Your Project:

[rspbot]

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