Editor code: tidy up BOOLs,NULLs and overrides pt2.

A few 'typedefs' replaced by 'using's
This shouldn't have any functional changes at all, just c++17 modernization
It's a part 2 of a split #2847

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

Code/Editor/Plugins/FFMPEGPlugin/main.cpp

@@ -15,7 +15,7 @@ PLUGIN_API IPlugin* CreatePluginInstance(PLUGIN_INIT_PARAM* pInitParam)
     if (pInitParam->pluginVersion != SANDBOX_PLUGIN_SYSTEM_VERSION)
     {
         pInitParam->outErrorCode = IPlugin::eError_VersionMismatch;
-        return 0;
+        return nullptr;
     }
 
     ModuleInitISystem(GetIEditor()->GetSystem(), "FFMPEGPlugin");