Fix sticky scroll performance issue by using correct array for min content width calculation

[Copilot]

Sticky scrolling was causing noticeable performance issues and stuttering during scroll operations due to inefficient DOM queries in the StickyScrollWidget._renderRootNode method.

Problem

The _renderRootNode method was calculating _minContentWidthInPx using the old this._renderedStickyLines array instead of the newly built renderedStickyLines array. This caused:

1. Performance degradation: Reading scrollWidth from potentially stale/removed DOM elements triggered unnecessary layout recalculations
2. Incorrect calculations: Using outdated scroll width values from elements that were being removed from the DOM
3. Browser frame drops: The additional layout work caused visible stuttering during scroll operations

Solution

Changed line 248 in stickyScrollWidget.ts to use the correct array and added proper empty array handling:

// Before (buggy):
this._minContentWidthInPx = Math.max(...this._renderedStickyLines.map(l => l.scrollWidth)) + layoutInfo.verticalScrollbarWidth;

// After (fixed):
this._minContentWidthInPx = renderedStickyLines.length > 0 
    ? Math.max(...renderedStickyLines.map(l => l.scrollWidth)) + layoutInfo.verticalScrollbarWidth 
    : 0;

Impact

• Performance: Eliminates forced layout recalculations by using fresh scroll width values that were already computed during rendering
• Accuracy: Ensures minimum content width calculation reflects the actual current DOM state
• User Experience: Reduces scroll stuttering and frame drops when sticky scroll is enabled
• Minimal Risk: Only 3 lines changed, preserving all existing functionality

The fix ensures that during sticky scroll updates, we use the scroll width values from the current rendering cycle instead of potentially accessing removed DOM elements.

Fixes #191973.

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