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/proxyaction.cpp

@@ -28,11 +28,7 @@
 using namespace Utils;
 
 ProxyAction::ProxyAction(QObject *parent) :
-    QAction(parent),
-    m_action(nullptr),
-    m_attributes(nullptr),
-    m_showShortcut(false),
-    m_block(false)
+    QAction(parent)
 {
     connect(this, &QAction::changed, this, &ProxyAction::updateToolTipWithKeySequence);
     updateState();