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/EditorFileMonitor.cpp

@@ -162,7 +162,7 @@ QString RemoveGameName(const QString &filename)
 void CEditorFileMonitor::OnFileMonitorChange(const SFileChangeInfo& rChange)
 {
     CCryEditApp* app = CCryEditApp::instance();
-    if (app == NULL || app->IsExiting())
+    if (app == nullptr || app->IsExiting())
     {
         return;
     }