Editor code: tidy up BOOLs,NULLs and overrides pt1.

A few 'typedefs' replaced by 'using's
This shouldn't have any functional changes at all, just c++17 modernization
It's a part 1 of a split #2847

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

Code/Editor/AzAssetBrowser/AzAssetBrowserWindow.cpp

@@ -42,7 +42,7 @@ public:
         AzToolsFramework::EditorEvents::Bus::Handler::BusConnect();
     }
 
-    ~ListenerForShowAssetEditorEvent()
+    ~ListenerForShowAssetEditorEvent() override
     {
         AzToolsFramework::EditorEvents::Bus::Handler::BusDisconnect();
     }