ProjectExplorer: Extend centralized state handling

Add some customization hooks to make tools aware of target errors
and vice versa.

Change-Id: I4d815087297a3fa1d1d6d52daeed7c4ae0f624bf
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/debugger/debuggerruncontrol.h

@@ -56,6 +56,7 @@ public:
     void prepare() override;
     void start() override;
     void stop() override;
+    void onTargetFailure() override;
 
     void handleFinished();