Core: Modernize

modernize-use-auto
modernize-use-nullptr
modernize-use-override
modernize-use-using
modernize-use-default-member-init (partially)

Change-Id: Idf10d7ffb1d98a04edc09a25c35e4e9e3abe87b5
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/coreplugin/helpmanager.h

@@ -56,7 +56,7 @@ public:
         ExternalHelpAlways = 3
     };
 
-    typedef QHash<QString, QStringList> Filters;
+    using Filters = QHash<QString, QStringList>;
 
     static HelpManager *instance();
     static QString collectionFilePath();