Debugger: Fix exit crash, dump QVariantList with gdb

Handle QVariantList within dumpers, as gdb does not resolve
typedefs. Disconnect the gdb process on exit, one more round
of event loop when quitting.

src/plugins/debugger/debuggerplugin.cpp

@@ -256,6 +256,7 @@ bool DebuggerListener::coreAboutToClose()
     if (answer == QMessageBox::No)
         return false;
     mgr->exitDebugger();
+    QCoreApplication::processEvents(QEventLoop::ExcludeUserInputEvents);
     return true;
 }