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/styleanimator.cpp

@@ -32,7 +32,7 @@
 Animation * StyleAnimator::widgetAnimation(const QWidget *widget) const
 {
     if (!widget)
-        return 0;
+        return nullptr;
     return Utils::findOrDefault(animations, Utils::equal(&Animation::widget, widget));
 }