Make highlights work for non-default settings in the profiles KCM

The recent QML port didn't implement the code that was required
for this to work. Here's the fix.

Using SettingStateBinding from kcmutils adds highlights to the
components within the QML page.

In order to also make the (non-)defaultIndicator in the sidebar
list view show up, System Settings needs to be able to construct
a single KCModuleData object through the KCM's plugin factory.
We need to register both the KQuickManagedConfigModule and the
KCModuleData when declaring the plugin, so instead of
K_PLUGIN_CLASS_WITH_JSON we now use K_PLUGIN_FACTORY_WITH_JSON.

ProfilesConfigKCM.{h,cpp} requires some refactoring to use a single
KCModuleData object instead of a collection of three different ones.
Instead of the ProfilesConfigKCM class owning three data objects,
it now only constructs a single one which in turn will create and
expose the KConfigXT-generated settings classes for all profiles.

BUG: 477848