Editor code: tidy up BOOLs,NULLs and overrides pt5. (#2876)

A few 'typedefs' replaced by 'using's
This shouldn't have any functional changes at all, just c++17 modernization
It's a part 5 of a split #2847

Signed-off-by: Nemerle <nemerle5+git@gmail.com>

Co-authored-by: Nemerle <nemerle5+git@gmail.com>

Code/Editor/EditorPreferencesDialog.cpp

@@ -282,7 +282,7 @@ void EditorPreferencesDialog::CreatePages()
     {
         auto pUnknown = classes[i];
 
-        IPreferencesPageCreator* pPageCreator = 0;
+        IPreferencesPageCreator* pPageCreator = nullptr;
         if (FAILED(pUnknown->QueryInterface(&pPageCreator)))
         {
             continue;