DAP: Add thread list

Change-Id: Ide9305e246f4e0dbe687e37a96b20e99b197ea3f
Reviewed-by: hjk <hjk@qt.io>

src/plugins/debugger/dap/dapengine.h

@@ -83,6 +83,7 @@ private:
     void handleDabConfigurationDone();
 
     void dabStackTrace();
+    void threads();
 
     void handleDapDone();
     void readDapStandardOutput();