Allow providing an error message from the application
Summary:
Allows us keep the message provided by QQuickWindow::sceneGraphError to later have on our bug reports.
https://doc.qt.io/qt-5/qquickwindow.html#sceneGraphError
These are generally problems at the OpenGL level that the user will usually be unable to take action on.
CCBUG: 375913
Test Plan: See D27985
Reviewers: Frameworks, sitter, dfaure
Reviewed By: dfaure
Subscribers: dfaure, kde-frameworks-devel
Tags: Frameworks
Differential Revision: https://phabricator.kde.org/D27986