[Backport 12.6] Channel settings dropdown display values not shown when using a ValueListProvider

See the report of this issue here: https://community.bloomreach.com/t/using-valuelistprovider-with-dropdownlist-in-channelinfo/183/3

The ValueListProvider can provide values for DropDowns in ComponentInfo and ChannelInfo classes. It seems that for ChannelInfo it stopped working correctly from 12.0. The TestSuite has an example implementation.