Don't crash on exit when a module attaches a menu item...

... such as Nyquist Workbench.

I don't fully understand why, but destroying the menu registry items very late,
during the destruction of static objects, causes a crash in memory deallocation,
at least on Mac.

So destroy the menu registry explicitly in application shut-down.

src/Menus.cpp

@@ -1059,6 +1059,11 @@ MenuTable::AttachedItem::AttachedItem(
    Registry::RegisterItem( sRegistry(), placement, std::move( pItem ) );
 }
 
+void MenuTable::DestroyRegistry()
+{
+   sRegistry().items.clear();
+}
+
 namespace {
 
 using namespace MenuTable;