Disconnect property changes from all pages when TabbedPage set to null

src/Controls/samples/Controls.Sample.UITests/Issues/Issue18457.cs

@@ -0,0 +1,44 @@
+using System;
+using System.Threading.Tasks;
+using Microsoft.Maui;
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Graphics;
+
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 18457, "Adding/Removing Pages From Removed TabbedPage Causes Crash")]
+public class Issue18457 : TestContentPage
+{
+    bool pagePushed = false;
+    TabbedPage _tabbedPage = new TabbedPage();
+	protected override void Init()
+	{
+        _tabbedPage.Children.Add(new ContentPage() { Title = "tab 1"});
+        _tabbedPage.Children.Add(new ContentPage() { Title = "tab 2"});
+        _tabbedPage.Children.Add(new ContentPage() { Title = "tab 3"});
+	}
+
+	protected override async void OnNavigatedTo(NavigatedToEventArgs args)
+	{
+		base.OnNavigatedTo(args);
+
+        if (!pagePushed)
+        {
+            pagePushed = true;
+            await Navigation.PushAsync(_tabbedPage);
+            await Navigation.PopAsync();
+            _tabbedPage.Children.Add(new ContentPage());
+            _tabbedPage.Children[0].Background = SolidColorBrush.Purple;
+            _tabbedPage.Children[0].Title = "update title";
+            _tabbedPage.Children[0].IconImageSource = "dotnet_bot.png";
+            await Task.Yield();
+            Content = new VerticalStackLayout(){
+                Children =
+                {
+                    new Label() { Text = "This test pushes and pops a TabbedPage, and then modifies the Children on the popped page."},
+                    new Label() { Text = "If the app doesn't crash, this test has passed.", AutomationId = "Success" }
+                }
+            };
+        }
+	}
+}

src/Controls/src/Core/Platform/Android/TabbedPageManager.cs

@@ -114,8 +114,9 @@ internal void SetElement(TabbedPage tabbedPage)
 			var activity = _context.GetActivity();
 			var themeContext = activity;
 
-			if (Element != null)
+			if (Element is not null)
 			{
+				Element.InternalChildren.ForEach(page => TeardownPage(page as Page));
 				((IPageController)Element).InternalChildren.CollectionChanged -= OnChildrenCollectionChanged;
 				Element.Appearing -= OnTabbedPageAppearing;
 				Element.Disappearing -= OnTabbedPageDisappearing;
@@ -124,7 +125,7 @@ internal void SetElement(TabbedPage tabbedPage)
 			}
 
 			Element = tabbedPage;
-			if (Element != null)
+			if (Element is not null)
 			{
 				_viewPager.LayoutChange += OnLayoutChanged;
 				Element.Appearing += OnTabbedPageAppearing;