debugger: move 'break by function' menu items

Move menu to from the main debug window to the context menu of the
breakpoints view to avoid clutter in the main menus.

src/plugins/debugger/breakwindow.h

@@ -50,6 +50,7 @@ signals:
     void breakpointDeleted(int index);
     void breakpointActivated(int index);
     void breakpointSynchronizationRequested();
+    void breakByFunctionRequested(const QString &functionName);
 
 private slots:
     void rowActivated(const QModelIndex &index);