Updates the PivotGridControl.
The LayoutChanged method recalculates all of the pivot grid's graphical information and redraws it. This method is automatically called when changes are applied to the control (for example, when the field width is changed, etc). This method can also be called manually when the pivot grid needs to be updated. This can be done when you need the control to be updated in response to custom actions that don't lead to automatic updating.