Dismiss any open content dialog when window is moved (#11485)

## Summary of the Pull Request
When the window moves, hide any visible content dialog (only one can be shown at a time) and ensure its associated async operation is terminated.

#10922 dismisses any open popups when the window is moved or any scroll viewer scrolls. However, if you just close a Popup from the UI tree, the async operation associated to a ContentDialog (started with `dialog.ShowAsync`) does not terminate. The dialog lock that prevents opening multiple dialogs at the same time is not released, and no further dialog can be shown. 
Explicitly dismissing the only visible ContentDialog using its `Hide` method terminates the operation.

## Validation Steps Performed
Manual tests, open up dialogs and move the window (like in #11425)

References #10922 
Closes #11425

src/cascadia/TerminalApp/AppLogic.cpp

@@ -375,6 +375,8 @@ namespace winrt::TerminalApp::implementation
             co_return ContentDialogResult::None;
         }
 
+        _dialog = dialog;
+
         // IMPORTANT: This is necessary as documented in the ContentDialog MSDN docs.
         // Since we're hosting the dialog in a Xaml island, we need to connect it to the
         // xaml tree somehow.
@@ -412,6 +414,16 @@ namespace winrt::TerminalApp::implementation
         // be released so another can be shown
     }
 
+    // Method Description:
+    // - Dismiss the (only) visible ContentDialog
+    void AppLogic::DismissDialog()
+    {
+        if (auto localDialog = std::exchange(_dialog, nullptr))
+        {
+            localDialog.Hide();
+        }
+    }
+
     // Method Description:
     // - Displays a dialog for errors found while loading or validating the
     //   settings. Uses the resources under the provided  title and content keys

src/cascadia/TerminalApp/AppLogic.h

@@ -106,6 +106,7 @@ namespace winrt::TerminalApp::implementation
         bool GetShowTitleInTitlebar();
 
         winrt::Windows::Foundation::IAsyncOperation<winrt::Windows::UI::Xaml::Controls::ContentDialogResult> ShowDialog(winrt::Windows::UI::Xaml::Controls::ContentDialog dialog);
+        void DismissDialog();
 
         Windows::Foundation::Collections::IMapView<Microsoft::Terminal::Control::KeyChord, Microsoft::Terminal::Settings::Model::Command> GlobalHotkeys();
 
@@ -132,6 +133,7 @@ namespace winrt::TerminalApp::implementation
         uint64_t _numOpenWindows{ 0 };
 
         std::shared_mutex _dialogLock;
+        winrt::Windows::UI::Xaml::Controls::ContentDialog _dialog;
 
         ::TerminalApp::AppCommandlineArgs _appArgs;
         ::TerminalApp::AppCommandlineArgs _settingsAppArgs;

src/cascadia/TerminalApp/AppLogic.idl

@@ -91,6 +91,7 @@ namespace TerminalApp
         // See IDialogPresenter and TerminalPage's DialogPresenter for more
         // information.
         Windows.Foundation.IAsyncOperation<Windows.UI.Xaml.Controls.ContentDialogResult> ShowDialog(Windows.UI.Xaml.Controls.ContentDialog dialog);
+        void DismissDialog();
 
         event Windows.Foundation.TypedEventHandler<Object, Windows.UI.Xaml.UIElement> SetTitleBarContent;
         event Windows.Foundation.TypedEventHandler<Object, String> TitleChanged;

src/cascadia/WindowsTerminal/AppHost.cpp

@@ -1316,6 +1316,11 @@ void AppHost::_WindowMoved()
 {
     if (_logic)
     {
+        // Ensure any open ContentDialog is dismissed.
+        // Closing the popup in the UI tree as done below is not sufficient because
+        // it does not terminate the dialog's async operation.
+        _logic.DismissDialog();
+
         const auto root{ _logic.GetRoot() };
 
         // This is basically DismissAllPopups which is also in