RFC: Deprecating KDesignerPlugin in favour of new ECMAddQtDesignerPlugin

[Friedrich W. H. Kossebau]

Hi,

following up on a recent discussion about kdesignerplugin currently providing 
a single Qt Designer plugin for all of those modules from KDE Frameworks which 
provide custom QWidgets, and with this coupling running against the idea of 
mpdularization with KDE Frameworks, a few patches have been sketched and made 
working to approach this.

Please see for discussion of problem and proposed solution with a series of 
patches this task:

    https://phabricator.kde.org/T11289

Please add your comments there, as well as on the patches, especially the 
proposed ECMAddQtDesignerPlugin addition to ECM.

If everyone agrees with the appraoch, would be material for KF 6.62 earliest 
(so only post upcoming KF 6.61).

Cheers
Friedrich