Utils: Modernize further

Many issues, mostly in headers, were not addressed in
e38410b76c

modernize-use-auto
modernize-use-nullptr
modernize-use-override
modernize-use-using
modernize-use-default-member-init
modernize-use-equals-default

Change-Id: I320a51726db881e582b898948d53735ebb06887a
Reviewed-by: hjk <hjk@qt.io>

src/libs/utils/shellcommand.h

@@ -63,7 +63,7 @@ private:
     void setFuture(QFutureInterface<void> *future);
 
     QFutureInterface<void> *m_future;
-    QMutex *m_futureMutex;
+    QMutex *m_futureMutex = nullptr;
     friend class ShellCommand;
 };