fabio_viewer does not launch with PySide 6

[ghisvail]

I believe the viewer needs a proper review of its compatibility with PySide 6.

On launch, there is an issue with QSizePolicy. When fixed, other issues come up.

[kif]

Thanks Ghislain for the report,

Indeed, the application was written for pyQt4 and now we are rather at Qt6 ... maybe it is a good issue for AI to upgrade the code.
Officially, at ESRF there is no willingness to upgrade the application.