Core: Replace ICoreListener by std::functions

ICoreListener::coreAboutToClose() remains in the core,
ICoreListener::editorAboutToClose() is handled by a new
EditorManager::addCloseEditorListener() function.

This removes the need for some boiler plate code resulting
from the need to implement the interface in custom classes
(DesignModeCoreListener, EditorClosingCoreListener,
PojectEplorer::CoreListener and VcsBase::CoreListener).

EditorManager::addCloseEditorListener

Change-Id: Ie554c987b5455b555be6d77b77e4013639201d22
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/plugins/coreplugin/mainwindow.h

@@ -40,6 +40,8 @@
 #include <QMap>
 #include <QColor>
 
+#include <functional>
+
 QT_BEGIN_NAMESPACE
 class QSettings;
 class QPrinter;
@@ -113,6 +115,8 @@ public:
     QStringList additionalAboutInformation() const;
     void appendAboutInformation(const QString &line);
 
+    void addPreCloseListener(const std::function<bool()> &listener);
+
 signals:
     void newItemDialogRunningChanged();
 
@@ -201,6 +205,7 @@ private:
 
     QToolButton *m_toggleSideBarButton;
     QColor m_overrideColor;
+    QList<std::function<bool()>> m_preCloseListeners;
 };
 
 } // namespace Internal