Clear the system menu when we refrigerate a window (#16225)

As in the title. Also fixes a crash for refrigeration with the rainbow
border.

Closes #16211

Tested by manually forcing us into Windows 10 mode (to refrigerate the
window). That immediately repros the bug, which was simple enough to
fix.

(cherry picked from commit d8c7719)
Service-Card-Id: 90928408
Service-Version: 1.19

src/cascadia/WindowsTerminal/AppHost.cpp

@@ -484,7 +484,7 @@ void AppHost::_revokeWindowCallbacks()
     // I suspect WinUI wouldn't like that very much. As such unregister all event handlers first.
     _revokers = {};
     _showHideWindowThrottler.reset();
-
+    _stopFrameTimer();
     _revokeWindowCallbacks();
 
     // DO NOT CLOSE THE WINDOW

src/cascadia/WindowsTerminal/IslandWindow.cpp

@@ -73,6 +73,8 @@ void IslandWindow::Refrigerate() noexcept
     // This pointer will get re-set in _warmInitialize
     SetWindowLongPtr(_window.get(), GWLP_USERDATA, 0);
 
+    _resetSystemMenu();
+
     _pfnCreateCallback = nullptr;
     _pfnSnapDimensionCallback = nullptr;
 
@@ -1917,6 +1919,12 @@ void IslandWindow::RemoveFromSystemMenu(const winrt::hstring& itemLabel)
     _systemMenuItems.erase(it->first);
 }
 
+void IslandWindow::_resetSystemMenu()
+{
+    // GetSystemMenu(..., true) will revert the menu to the default state.
+    GetSystemMenu(_window.get(), TRUE);
+}
+
 void IslandWindow::UseDarkTheme(const bool v)
 {
     const BOOL attribute = v ? TRUE : FALSE;

src/cascadia/WindowsTerminal/IslandWindow.h

@@ -159,6 +159,7 @@ class IslandWindow :
 
     std::unordered_map<UINT, SystemMenuItemInfo> _systemMenuItems;
     UINT _systemMenuNextItemId;
+    void _resetSystemMenu();
 
 private:
     // This minimum width allows for width the tabs fit