filechooserbutton: For the open-dialog-cancel-* tests, add a real nomenclature and...

filechooserbutton: For the open-dialog-cancel-* tests, add a real nomenclature and test all the combinations

We used to have numeric names, which are a pain to maintain when new tests are added.
Now we have a real nomenclature (see the comment at the beginning of the open-dialog-cancel-* tests),
which lets us see easily if we have tested all the combinations.

Also, added all the combinations that were missing and removed redundant tests.
Not all the tests pass currently.

Signed-off-by: Federico Mena Quintero <federico@gnome.org>