fix: Scrolling reliability

[MartinZikmund]

GitHub Issue: closes #

PR Type:

What is the current behavior? 🤔

Improve scrolling reliability before #22873

What is the new behavior? 🚀

PR Checklist ✅

Please check if your PR fulfills the following requirements:

• 📝 Commits must be following the Conventional Commits specification.
• 🧪 Added Runtime tests, UI tests, or a manual test sample for the changes have been added (for bug fixes / features) (if applicable)
• 📚 Docs have been added/updated which fit documentation template (for bug fixes / features)
• 🖼️ Validated PR Screenshots Compare Test Run results.
• ❗ Contains NO breaking changes

Other information ℹ️

[Copilot]

Pull request overview

This PR adjusts ScrollViewer’s deferred intermediate scrolling updates to be scheduled at normal dispatcher priority (instead of idle) to improve update reliability during sustained scrolling.

Changes:

• Switch deferred update scheduling from Dispatcher.RunIdleAsync(...) to Dispatcher.RunAsync(CoreDispatcherPriority.Normal, ...) in ScrollViewer.RequestUpdate().

Comments suppressed due to low confidence (1)

src/Uno.UI/UI/Xaml/Controls/ScrollViewer/ScrollViewer.cs:1333

• In RequestUpdate(), _hasPendingUpdate is set to true only after scheduling the dispatcher callback. If the dispatcher implementation ever executes the callback synchronously (e.g., via a custom CoreDispatcher.DispatchOverride in some hosts/tests), the callback can observe _hasPendingUpdate == false, skip Update(...), and then _hasPendingUpdate becomes true with no further callback queued (updates can get stuck). Set _hasPendingUpdate = true before calling Dispatcher.RunAsync(...) to make the ordering robust.

			_ = Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
			{
				if (_hasPendingUpdate)
				{
					Update(isIntermediate: true);
				}
			});
			_hasPendingUpdate = true;
		}

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