Fix nuxeo-directory-radio-group element in import tab when setting properties on multiple files

When importing multiple files in the IMPORT tab in the Web UI, if element nuxeo-directory-radio-group is used for a property, selecting a value for one file applies to all files instead of only on the single file.

How to reproduce:

• define a new document type in Studio modeler with a directory property (e.g. on directory country)
• in Studio Designer use element nuxeo-directory-radio-group for the custom property in layout import
• deploy
• log in the Web UI
• navigate to a folder
• click on the + icon to create a document and open tab IMPORT
• drag and drop 2 files, click on ADD PROPERTIES button and select the new document type
• select Africa/Algeria in the custom field for the first file
• click on button EDIT NEXT and select Africa/Angola for the second file
• click on EDIT PREVIOUS to come back to the first file

Expected result: custom field shows Africa/Algeria selected.
Actual result: custom field shows Africa/Angola selected, like the last selected value applies to all files.