Dismiss flyouts before opening warning dialog when exiting app (#16075)

Updated the function `TerminalPage::CloseWindow` to include logic for
closing context and flyout menus so that they are dismissed before the
warning is displayed.

Closes #16039

(cherry picked from commit aafb917)
Service-Card-Id: 90731988
Service-Version: 1.18

Author: codecruisedor

src/cascadia/TerminalApp/TerminalPage.cpp

@@ -1941,6 +1941,11 @@ namespace winrt::TerminalApp::implementation
             _settings.GlobalSettings().ConfirmCloseAllTabs() &&
             !_displayingCloseDialog)
         {
+            if (_newTabButton && _newTabButton.Flyout())
+            {
+                _newTabButton.Flyout().Hide();
+            }
+            _DismissTabContextMenus();
             _displayingCloseDialog = true;
             auto warningResult = co_await _ShowCloseWarningDialog();
             _displayingCloseDialog = false;