fix: Prevent page scroll when hovering chart tooltip

[Who-is-PS]

Description

Hovering a chart with multiple series causes the entire page to scroll unexpectedly. This happens because scrollIntoViewNearestContainer in src/internal/utils/dom.ts falls back to document.documentElement when no scrollable parent is found, causing .scrollTo() to scroll the whole page.

The issue is triggered by series-details/index.tsx, which calls scrollIntoViewNearestContainer with scrollMode: "always" every time a tooltip appears with a highlighted series item. When the tooltip content area isn't inside a scrollable container, the fallback to documentElement scrolls the page instead.

Fix

Return early when getScrollParent() finds no scrollable ancestor, instead of falling back to document.documentElement. If there's no scrollable container, there's nothing to scroll into view.

Related links, issue #, if available: n/a

• Regression from fix: Avoid scrolling the entire page for charts with many series #134
• AWSUI-61501

How has this been tested?

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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