Avoid redundant breadcrumbs scroll updates while preserving revealLast UX

[Copilot]

Description

The perf sample points to breadcrumb reveal work on editor-open/update paths.
After feedback, the fix was adjusted to preserve existing revealLast() UX (including behavior related to #168824) while still removing redundant hot-path work.

Changes made

• Kept revealLast() using non-minimal reveal semantics:

  revealLast(): void {
  	this._reveal(this._items.length - 1, false);
  }

• Optimized _reveal(...) to no-op when the target item is already aligned:
  • Early return when node.offsetLeft === scrollLeft
  • This avoids unnecessary setScrollPosition/scroll-toggle calls without changing reveal behavior.

Test updates

• Replaced the focused test with one that validates no scroll update is performed when already aligned:
  • src/vs/base/test/browser/ui/breadcrumbs/breadcrumbsWidget.test.ts

Testing

• npm run transpile-client
• node test/unit/browser/index.js --run src/vs/base/test/browser/ui/breadcrumbs/breadcrumbsWidget.test.ts --browser chromium
• npm run compile-check-ts-native

[dmitrivMS]

@copilot Are you sure about the root cause?
Also, won't it make it even worse UX - see #168824 which you are also fixing...

[Copilot]

@copilot Are you sure about the root cause?
Also, won't it make it even worse UX - see #168824 which you are also fixing...

You’re right to call that out. I adjusted this in 00075f3e.

I reverted revealLast() to non-minimal reveal (to avoid regressing #168824 behavior), and moved the perf optimization to _reveal: it now early-returns when node.offsetLeft === current scrollLeft, so we skip redundant scroll updates in the hot path without changing reveal semantics.

[dmitrivMS]

Closing in favor of #315385, which folds in the same "skip redundant scroll update when aligned" optimization (generalized via getBreadcrumbScrollLeft so it covers minimal and non-minimal reveal paths) and additionally fixes the right-clipping reveal bug. The UX behavior from #168824 is preserved there as well.