ImageJ display should use convertService

When checking if we have a display for a given object, the `ConvertService` should be used to check if we can convert from the given type to a supported type

Start at the ImageJ display check and trace how the ConvertService is accessed to determine whether an object can become a supported display type. Done means display availability is decided by conversion capability for the given object type; no file or test is named in the issue, so locate the relevant implementation and tests first.

Written by the indexing model from the issue text.