Add MapImageLayer as Input for Custom Search Source

nadja

The search widget is a powerful tool for interacting with the displayed layer. Currently neither MapImageLayer nor their sublayers can be loaded directly. Currently we need to load the same source once as a MapImageLayer to benefit from the server-side rendering/fast display of many features and once as a Feature Layer to make it searchable. We would like to use the MapImageLayer as input for our custom search source.