Restore absent result selection actions for collections

Prior to NXP-25345, actions contributed to RESULTS_SELECTION_ACTIONS were also available when custom selection actions were contributed to nuxeo-results (i.e. adding COLLECTION_ACTIONS). However, now COLLECTION_ACTIONS simple override RESULTS_SELECTION_ACTIONS, making these actions disappear on collections.

A possible fix here is to contribute the actions on RESULTS_SELECTION_ACTIONS to COLLECTION_ACTIONS as well.