object_validators: Group common fields in CommonValidations

Notes:
- QuestionValidator didn't have a :name field but that seems like a mistake
- `_fields` functions can't inherit others because of some Validators
- bto/bcc fields were absent in activities, also seems like a mistake
  (Well IIRC we don't or barely support bto/bcc anyway)

test/pleroma/web/activity_pub/transmogrifier/add_remove_handling_test.exs

@@ -67,7 +67,9 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier.AddRemoveHandlingTest do
       "target" => "https://example.com/users/lain/collections/featured",
       "type" => "Add",
       "to" => [Pleroma.Constants.as_public()],
-      "cc" => ["https://example.com/users/lain/followers"]
+      "cc" => ["https://example.com/users/lain/followers"],
+      "bcc" => [],
+      "bto" => []
     }
 
     assert {:ok, activity} = Transmogrifier.handle_incoming(message)
@@ -82,7 +84,9 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier.AddRemoveHandlingTest do
       "target" => "https://example.com/users/lain/collections/featured",
       "type" => "Remove",
       "to" => [Pleroma.Constants.as_public()],
-      "cc" => ["https://example.com/users/lain/followers"]
+      "cc" => ["https://example.com/users/lain/followers"],
+      "bcc" => [],
+      "bto" => []
     }
 
     assert {:ok, activity} = Transmogrifier.handle_incoming(remove)
@@ -161,7 +165,9 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier.AddRemoveHandlingTest do
       "target" => "https://#{host}/users/#{user.nickname}/collections/featured",
       "type" => "Add",
       "to" => [Pleroma.Constants.as_public()],
-      "cc" => ["https://#{host}/users/#{user.nickname}/followers"]
+      "cc" => ["https://#{host}/users/#{user.nickname}/followers"],
+      "bcc" => [],
+      "bto" => []
     }
 
     assert {:ok, activity} = Transmogrifier.handle_incoming(message)