Harmonize GridLayout2 and GridData2 with SWT classes

Similar to https://github.com/eclipse-windowbuilder/windowbuilder/issues/963, the [GridLayout2](https://github.com/eclipse-windowbuilder/windowbuilder/blob/master/org.eclipse.wb.rcp/src/org/eclipse/wb/internal/rcp/model/layout/grid/GridLayout2.java) and [GridData2](https://github.com/eclipse-windowbuilder/windowbuilder/blob/master/org.eclipse.wb.rcp/src/org/eclipse/wb/internal/rcp/model/layout/grid/GridData2.java) are old copies of the SWT layouts, which store additional information that are relevant during design time.

We should separate the designer information from the layout algorithm to make sure that our implementation matches the actual implementation.