fix(RAC): use ICB size as the fallback value for visual viewport

[lixiaoyan]

Per spec, the visual viewport size does not include the scrollbar. Instead of window.innerWidth/Height, we should use document.documentElement.clientWidth/Height (which is equivalent to the ICB size) as the fallback value.

See: https://drafts.csswg.org/cssom-view/#visualViewport

✅ 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:

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