{Tree,Table}: Add cell rect accessor.

BColumnListView:
- Add helper method for getting the visible rect of a given field.
  Refactor SuggestTextPosition to use it.

{Tree,Table}:
- Add wrapper to retrieve table cell rect using the aforementioned
  BCLV helper.

headers/private/interface/ColumnListView.h

@@ -363,6 +363,9 @@ public:
 			BPoint				SuggestTextPosition(const BRow* row,
 									const BColumn* column = NULL) const;
 
+			BRect				GetFieldRect(const BRow* row,
+									const BColumn* column) const;
+
 			void				SetLatchWidth(float width);
 			float				LatchWidth() const;
 	virtual	void				DrawLatch(BView* view, BRect frame,