[bug#48627] Qt6 Base and Module Updates

[Eric Brown]

Hello All,

This is the first email introducing a patch set for Qt6 updates.  Maxim Couyer 
did the hard work of patching qtbase and showing a way to migrate gradually 
away from Qt5 (sorry this is not branched off those patches).  The other 
patches aim to replace existing Qt5 packages with their Qt6 analogues, and also 
add the Qt5Compat module.

In subsequent patches, I would like to complete the additional modules which 
round out Qt 6.1.0 "everywhere" .

Known issues:
* qtcontrols2 and qtdatavis3d do not build but I think need a few tweaks 
potentially identified in Qt bugtracker.

Best regards,
Eric