The LayoutItemProxy is a proxy for an arbitrary QuickItem that is
intended to be used in Layouts. This allows to position a QuickItem
in multiple layouts to build responsive layouts.
[ChangeLog][Layouts] Added LayoutItemProxy, a helper item for writing
responsive layouts.
Task-number: QTBUG-71153
Change-Id: Ief2bdbf44b3b346157ce2c71a313cc1e132f49ac
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>