Add a menu entry for copying system information

Which outputs the information from qtdiag, installed plugins,
and general Qt Creator build information.

Task-number: QTCREATORBUG-16135
Change-Id: I618b9883369bae45006bb109f8757e89b091b882
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/coreplugin/icore.h

@@ -130,6 +130,8 @@ public:
 
     static void addPreCloseListener(const std::function<bool()> &listener);
 
+    static QString systemInformation();
+
 public slots:
     static void saveSettings();