[SHELL32] Enable _DEBUG and fix assertion failures (#4307)

Improve debuggability. Fix "WorkerW" window class conflict.
- Enable _DEBUG macro if debugging, in order to enable ATLASSERT macro.
- Fix assertion failures.
- Add SHCreateDefaultWorkerWindow helper function and CWorkerTraits, then use them.
- Don't create the broker and server windows by themselves, but subclass.
CORE-17505, CORE-13950

dll/win32/shell32/CDefView.cpp

@@ -1027,7 +1027,8 @@ HRESULT CDefView::FillList()
 
 LRESULT CDefView::OnShowWindow(UINT uMsg, WPARAM wParam, LPARAM lParam, BOOL &bHandled)
 {
-    m_ListView.UpdateWindow();
+    if (m_ListView.IsWindow())
+        m_ListView.UpdateWindow();
     bHandled = FALSE;
     return 0;
 }