fix: Make NavigationView Settings item selectable

- Fixes #4809 - in some cases on some Uno targets, the lifecycle events are in such order that causes presenters of dynamically added NavigationViewItems not to be initialized properly. These changes work around this problem when selection indicator is requeste. These changes can be reverted when #4689 is fixed.

Author: MartinZikmund

src/Uno.UI/Microsoft/UI/Xaml/Controls/NavigationView/NavigationViewItemPresenter.cs

@@ -39,6 +39,16 @@ protected override void OnApplyTemplate()
 			var navigationViewItem = GetNavigationViewItem();
 			if (navigationViewItem != null)
 			{
+#if IS_UNO
+				// TODO: Uno specific: We may be reapplying the template, in which case
+				// we need to unsubscribe the previous Tapped event handler.
+				// Can be removed when #4689.
+				if (m_expandCollapseChevron != null)
+				{
+					m_expandCollapseChevron.Tapped -= navigationViewItem.OnExpandCollapseChevronTapped;
+				}
+#endif
+
 				var expandCollapseChevron = GetTemplateChild(c_expandCollapseChevron) as Grid;
 				if (expandCollapseChevron != null)
 				{
@@ -87,7 +97,19 @@ internal void RotateExpandCollapseChevron(bool isExpanded)
 
 		internal UIElement GetSelectionIndicator()
 		{
-			return m_helper.GetSelectionIndicator();
+#if IS_UNO
+			// TODO: Uno specific: This is done to ensure that the presenter
+			// was initialized properly - if helper is not null, but content grid
+			// is null, it means the presenter was not initialized correctly.
+			// Can be removed when #4809 is fixed.
+			if (m_contentGrid == null && m_helper != null)
+			{
+				// Reinitialize
+				OnApplyTemplate();
+			}
+#endif
+			// m_helper could be null here, if template was not yet applied
+			return m_helper?.GetSelectionIndicator();
 		}
 
 		protected override bool GoToElementStateCore(string state, bool useTransitions)