[iOS/Mac] Fixed OnBackButtonPressed not firing for Shell Navigation Bar Button (#34401)

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### Issue Details
The OnBackButtonPressed override is not triggered when the back button
in the Shell Navigation Bar is clicked.

### Root Cause
The ShouldPopItem method (called by iOS navigation bar when the back
button is tapped) calls SendPop(), which only checks for
BackButtonBehavior.Command but never calls Page.SendBackButtonPressed().

### Description of Change
Added SendBackButtonPressed() check inside the tracker loop in
SendPop(), after the existing BackButtonBehavior.Command check, before
the break.

### Validated the behaviour in the following platforms
- [ ] Android
- [ ] Windows
- [x] iOS
- [x] Mac


### Issues Fixed:
Fixes #34190 

### Screenshots
| Before  | After |
|---------|--------|
|  <video
src="https://github.com/user-attachments/assets/6987afb2-8a0d-4bb0-aa49-8f5b53931bae">
|   <video
src="https://github.com/user-attachments/assets/a32ed322-7ec4-44f4-94de-dc56c191a79f"> 
|

Author: Dhivya-SF4094

src/Controls/src/Core/Compatibility/Handlers/Shell/iOS/ShellSectionRenderer.cs

@@ -144,6 +144,12 @@ internal bool SendPop(UIViewController topViewController = null)
 						return false;
 					}
 
+					// Allow the page to intercept back navigation via OnBackButtonPressed
+					if (tracker.Value.Page?.SendBackButtonPressed() == true)
+					{
+						return false;
+					}
+
 					break;
 				}
 			}

src/Controls/tests/TestCases.HostApp/Issues/Issue33523.cs

@@ -2,7 +2,7 @@
 
 namespace Maui.Controls.Sample.Issues
 {
-	[Issue(IssueTracker.Github, 33523, "OnBackButtonPressed not firing for Shell Navigation Bar button in .NET 10 SR2", PlatformAffected.Android)]
+	[Issue(IssueTracker.Github, 33523, "OnBackButtonPressed not firing for Shell Navigation Bar button in .NET 10 SR2", PlatformAffected.Android | PlatformAffected.iOS | PlatformAffected.MacCatalyst)]
 	public class Issue33523 : Shell
 	{
 		public Issue33523()

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue33523.cs

@@ -1,5 +1,3 @@
-#if TEST_FAILS_ON_CATALYST && TEST_FAILS_ON_IOS // Issue: https://github.com/dotnet/maui/issues/34190
-
 using NUnit.Framework;
 using UITest.Appium;
 using UITest.Core;
@@ -26,19 +24,20 @@ public void OnBackButtonPressedShouldFireForShellNavigationBarButton()
 			// Verify initial state
 			var statusLabel = App.WaitForElement("StatusLabel");
 			Assert.That(statusLabel.GetText(), Is.EqualTo("OnBackButtonPressed not called"));
-
-			// Tap the navigation bar back button
-			// Note: This uses the Shell's navigation bar back button, not the system back button
-			App.TapBackArrow();
-
-			// Wait a moment for the event to fire
+			if (App is AppiumIOSApp iosApp && HelperExtensions.IsIOS26OrHigher(iosApp))
+			{
+				App.TapBackArrow(); // In iOS 26, the previous page title is not shown along with the back arrow, so we use the default back arrow
+			}
+			else
+			{
+				App.TapBackArrow(Device is TestDevice.iOS or TestDevice.Mac ? "Main Page" : "");
+			}
 			App.WaitForElement("StatusLabel");
 
 			// Verify OnBackButtonPressed was called
 			statusLabel = App.FindElement("StatusLabel");
-			Assert.That(statusLabel.GetText(), Is.EqualTo("OnBackButtonPressed was called"), 
+			Assert.That(statusLabel.GetText(), Is.EqualTo("OnBackButtonPressed was called"),
 				"OnBackButtonPressed should be called when tapping the Shell Navigation Bar back button");
 		}
 	}
 }
-#endif