file mime-type is not set when using the import mode

When enabling "Apply Date, Author and Dublin Core properties.", the files attached to "file:content" don't have a mime-type after import, resulting in failed thumbnail generation

If the import mode is not activated, then the mime-type is set correctly by the platform.

In the code it looks like file:content is treated differently than other blob properties and cannot accept an object including the mime-type like described at https://doc.nuxeo.com/nxdoc/nuxeo-csv/#files-attachment. Thus there is no workaround.

https://github.com/nuxeo/nuxeo/blob/34467b1be29c8b5af71fdcb518214aa592d36ae2/addons/nuxeo-csv/nuxeo-csv-core/src/main/java/org/nuxeo/ecm/csv/core/CSVImporterWork.java#L459