Debugger: Remove most remaining occurrences of WatchData

... in WatchHandler and DebuggerEngine interface.
Adjust using code.

Change-Id: I6371f3e96ba46a783e23a5767cdde24a10d3fce7
Reviewed-by: Christian Stenger <christian.stenger@theqtcompany.com>
Reviewed-by: hjk <hjk@theqtcompany.com>

src/libs/utils/treemodel.h

@@ -88,6 +88,7 @@ public:
     void appendChild(TreeItem *item);
     void insertChild(int pos, TreeItem *item);
     void removeChildren();
+    void sortChildren(const std::function<bool(const TreeItem *, const TreeItem *)> &cmp);
     void update();
     void updateColumn(int column);
     void expand();