kcms/tabbox: Expose shortcuts as a KConfigSkeleton
Provide a new KConfigSkeleton (ShortcutSettings) so that the KCModuleData knows if any of the shortcuts is non-default.
This improves the UX by showing an "orange dot" in system settings when just a shorcut has been changed.
Note to show the orange ring around the shortcut widget, this commit is required frameworks/kxmlgui@47572c26 but it's only on KF6 branch
We also need to implement a new specific KConfigSkeletonItem
(ShortcutItem
) that uses KGlobalAccel to retrieve and store
the shortcuts, instead of storing them in a config file.