fix(overlays): cap visualViewport width at clientWidth to handle scrollbar gutter

[hasegawa-101]

Closes #9199

✅ 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

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[nwidynski]

This should probably be rounded to account for sub-pixel differences when zooming.

[snowystinger]

shouldn't it be ceil? or floor? I don't quite follow what the concern is here though

also, this doesn't need to be an if, can be

width = Math.min(Math.round(width), documentElement.clientWidth)

[nwidynski]

Concern were false-positives in general. I did not take a deeper look at the underlying issue before, but in this case false-positives could result in a tiny gap between the overlay and scrollbar, right? Maybe that's acceptable though - certainly better than cutting content off 🤷

On Firefox & Chrome the clientWidth appears to correspond to Math.round, but Safari apparently uses some other heuristic, neither floor nor ceil.