fix: Ensure ShowAsync returns if popup is forcibly closed

Author: kazo0

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Controls/Given_ContentDialog.cs

@@ -327,6 +327,56 @@ public async Task When_BackButton_Pressed(bool isCloseButtonEnabled)
 				SUT.Hide();
 			}
 		}
+
+		[TestMethod]
+#if __MACOS__
+		[Ignore("Currently fails on macOS, part of #9282 epic")]
+#endif
+		public async Task When_Popup_Closed()
+		{
+			var closedEvent = new Event();
+			var openedEvent = new Event();
+			var closedRegistration = new SafeEventRegistration<ContentDialog, TypedEventHandler<ContentDialog, ContentDialogClosedEventArgs>>("Closed");
+			var openedRegistration = new SafeEventRegistration<ContentDialog, TypedEventHandler<ContentDialog, ContentDialogOpenedEventArgs>>("Opened");
+
+			var SUT = new MyContentDialog
+			{
+				Title = "Dialog title",
+				Content = "Dialog content",
+				CloseButtonText = "Close",
+			};
+
+			closedRegistration.Attach(SUT, (s, e) => closedEvent.Set());
+			openedRegistration.Attach(SUT, (s, e) => openedEvent.Set());
+
+			try
+			{
+				var showAsyncResult = SUT.ShowAsync().AsTask();
+
+				await openedEvent.WaitForDefault();
+
+				SUT._popup.IsOpen = false;
+
+				await closedEvent.WaitForDefault();
+
+				VERIFY_IS_TRUE(closedEvent.HasFired());
+				VERIFY_IS_FALSE(SUT._popup.IsOpen);
+
+				if (await Task.WhenAny(showAsyncResult, Task.Delay(2000)) == showAsyncResult)
+				{
+					var dialogResult = showAsyncResult.Result;
+					VERIFY_ARE_EQUAL(ContentDialogResult.None, dialogResult);
+				}
+				else
+				{
+					Assert.Fail("Timed out waiting for ShowAsync");
+				}
+			}
+			finally
+			{
+				SUT.Hide();
+			}
+		}
 #endif
 
 #if __ANDROID__
@@ -379,6 +429,7 @@ void OnShowing(InputPane sender, InputPaneVisibilityEventArgs args)
 				inputPane.Showing -= OnShowing;
 			}
 			await WindowHelper.WaitForIdle();
+			await WindowHelper.WaitForIdle();
 		}
 
 		private static async Task ShowDialog(MyContentDialog dialog)

src/Uno.UI/UI/Xaml/Controls/ContentDialog/ContentDialog.cs

@@ -70,6 +70,15 @@ public ContentDialog() : base()
 					that.UpdateVisualState();
 				}
 			};
+
+			_popup.Closed += (s, e) =>
+			{
+				if (thisRef.Target is ContentDialog that)
+				{
+					that.Hide();
+				}
+			};
+
 			this.KeyDown += OnPopupKeyDown;
 			var inputPane = InputPane.GetForCurrentView();
 			inputPane.Showing += (o, e) =>