Debugger: Make the time stamp recording option work for single items

Should help to drill down to individual expensive dumpers.

Change-Id: I983ba075231784f71dd9d5c3bda375a3ee508bf6
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/debugger/watchdata.h

@@ -99,6 +99,7 @@ public:
     bool            valueEnabled;  // Value will be enabled or not
     bool            valueEditable; // Value will be editable
     bool            outdated;      // \internal item is to be removed.
+    double          time = 0;      // Time used on the dumper side to produce this item
 
 private:
     void parseHelper(const GdbMi &input, bool maySort);