feat: fire user.Deactivating from the admin deactivate action

- DeactivatingEvent and DeactivatingEventName in classes
- FireDeactivatingEvent modelled on FireDeletingEvent
- the deactivate bulk action runs DeactivateUsers unchanged, then fires
  the event per newly deactivated user in the action's transaction

controllers/users_admin_controller.go

@@ -594,13 +594,35 @@ func (c usersAdminController) AdminBulkActions() []pact.AdminBulkAction {
 	}
 	return []pact.AdminBulkAction{
 		bulk("activate", classes.ActivateUsers),
-		bulk("deactivate", classes.DeactivateUsers),
+		bulk("deactivate", c.deactivateUsers),
 		bulk("restore", classes.RestoreUsers),
 		bulk("ban", classes.BanUsers),
 		bulk("unban", classes.UnbanUsers),
 	}
 }
 
+// deactivateUsers runs classes.DeactivateUsers unchanged and then fires
+// user.Deactivating, in the action's transaction, for every selected user
+// that was not deactivated before. A listener error rolls the action back.
+func (c usersAdminController) deactivateUsers(ctx context.Context, tx *gorm.DB, users []*models.User) (int, error) {
+	pending := make([]*models.User, 0, len(users))
+	for _, user := range users {
+		if user != nil && user.ID != 0 && !user.DeletedAt.Valid {
+			pending = append(pending, user)
+		}
+	}
+	changed, err := classes.DeactivateUsers(ctx, tx, users)
+	if err != nil {
+		return 0, err
+	}
+	for _, user := range pending {
+		if err := FireDeactivatingEvent(ctx, c.application(), user, tx); err != nil {
+			return 0, err
+		}
+	}
+	return changed, nil
+}
+
 // throttleState reads whether one user is banned and whether they are
 // suspended, through the write's transaction when there is one.
 func (c usersAdminController) throttleState(ctx context.Context, userID uint) (banned, suspended bool, err error) {