This patch caches the last image from a document/model.
The result ist that when reopening a file in the 3D editor
the user sees immediately something.
Since the view is not interactive, yet, we show a busy indicator
until the view is fully initialized.
Change-Id: I26c8b0ea69f98ceb41580624c51d48d1e633ab80
Reviewed-by: Mahmoud Badri <mahmoud.badri@qt.io>
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
