FIX: Various invite system fixes (#13003)

* FIX: Ensure the same email cannot be invited twice

When creating a new invite with a duplicated email, the old invite will
be updated and returned. When updating an invite with a duplicated email
address, an error will be returned.

* FIX: not Ember helper does not exist

* FIX: Sync can_invite_to_forum? and can_invite_to?

The two methods should perform the same basic set of checks, such as
check must_approve_users site setting.

Ideally, one of the methods would call the other one or be merged and
that will happen in the future.

* FIX: Show invite to group if user is group owner

app/serializers/current_user_serializer.rb

@@ -65,7 +65,12 @@ class CurrentUserSerializer < BasicUserSerializer
              :can_review,
 
   def groups
-    object.visible_groups.pluck(:id, :name).map { |id, name| { id: id, name: name } }
+    owned_group_ids = GroupUser.where(user_id: id, owner: true).pluck(:group_id).to_set
+    object.visible_groups.pluck(:id, :name).map do |id, name|
+      group = { id: id, name: name }
+      group[:owner] = true if owned_group_ids.include?(id)
+      group
+    end
   end
 
   def link_posting_access