better fix: nested grid size issue

[adumesny]

Description

• fix Widget width reported incorrectly by save() after dragging from wider nested grid #2394]
• better fix that makes sure we keep wanted size when an item is dropped on us (so we remember in case we change grid column)
• also changed to not save x,y during dropping since the drag behavior will figure where to put it, and that means we don't cache that layout that might not apply to the new grid anyway.
• added a running example showing issue.

Checklist

• Created tests which fail without the change (if possible)
• All tests passing (yarn test)
• Extended the README / documentation, if necessary