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

[lixiaoyan]

According to the specification, the visual viewport size excludes the scrollbar. Instead of window.innerWidth/Height, the fallback value should be document.documentElement.clientWidth/Height, which is the same as the ICB size and almost equivalent to the visual viewport size, which excludes the scrollbar.

It's mainly a fix about code correctness, as the VisualViewport is widely supported today.

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:

🧢 Your Project:

[lixiaoyan]

Edited: I've updated the PR description.

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Original post

@snowystinger This PR is primarily about correctness. It may not address any real-world issues because the VisualViewport is widely supported today.

[snowystinger]

Team, do we care about the fallback for this?

discussed, this is fine to go in