Manage long text in aggregation filters (nuxeo-dropdown-aggregation)

Steps to reproduce:

1. create a user whose first name is Johnny and last name is "Hasaveryveryverylonglastnamefortestingpurpose"
2. log in with this user
3. go to the personal workspace
4. add all the possible columns to the content view => the goal is to have narrow columns
5. click on the filter for the Contributors colum and select "Johnny Hasaveryveryverylonglastnamefortestingpurpose"
6. Observe that it's not possible to see the entire value in the filter box, as you can see on the attached screenshot

Expected behavior: the entire value selected in the filter can be seen, maybe by using a horizontal scrollbar