Previously, icon generation was done at import time, but that was
wasteful, as we now have image cache backed icon generation
available for component library icons. Added the few remaining missing
bits to support icon generation for image cache and disabled the old
icon generation implementation for Qt6.
A few issues in fit algorithm for preview image generation were also
uncovered and fixed to make icons render scene in comparable size to
the old version.
Qt5 imports still generate using old way since component library
3D previews generation doesn't work on Qt5.
Fixes: QDS-6205
Change-Id: I5418fa19d86e81adcd184be023f1dfbc813d0bf5
Reviewed-by: Mahmoud Badri <mahmoud.badri@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Samuel Ghinet <samuel.ghinet@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
80ea026fd8