types: Add EditHistoryEvent and APIEditHistoryEvent types.

These types will help make iteration on this code easier.

Note that `user_id` can be null due to the fact that
edit history entries before March 2017 did not log
the user that made the edit, which was years after
supporting topic edits (discovered in test deployment
of migration on chat.zulip.org).

Co-authored-by: Lauryn Menard <lauryn.menard@gmail.com>

zerver/lib/topic.py

@@ -8,6 +8,7 @@ from sqlalchemy.sql import ColumnElement, column, func, literal
 from sqlalchemy.types import Boolean, Text
 
 from zerver.lib.request import REQ
+from zerver.lib.types import EditHistoryEvent
 from zerver.models import Message, Stream, UserMessage, UserProfile
 
 # Only use these constants for events.
@@ -135,11 +136,11 @@ def user_message_exists_for_topic(
 
 
 def update_edit_history(
-    message: Message, last_edit_time: datetime, edit_history_event: Dict[str, Any]
+    message: Message, last_edit_time: datetime, edit_history_event: EditHistoryEvent
 ) -> None:
     message.last_edit_time = last_edit_time
     if message.edit_history is not None:
-        edit_history = orjson.loads(message.edit_history)
+        edit_history: List[EditHistoryEvent] = orjson.loads(message.edit_history)
         edit_history.insert(0, edit_history_event)
     else:
         edit_history = [edit_history_event]
@@ -154,7 +155,7 @@ def update_messages_for_topic_edit(
     topic_name: Optional[str],
     new_stream: Optional[Stream],
     old_stream: Stream,
-    edit_history_event: Dict[str, Any],
+    edit_history_event: EditHistoryEvent,
     last_edit_time: datetime,
 ) -> List[Message]:
     propagate_query = Q(recipient_id=old_stream.recipient_id, subject__iexact=orig_topic_name)