Refactored the existing 3D node preview generation to be done
synchronously, which enables their use also for creating state
and item library previews for 3D nodes with ease.
Fixes: QDS-5785
Change-Id: Ib493eccbc239f33bcad3301673a865494616a901
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>