Handle all entity types on isinstance checks

Only the uses of `isinstance` against `InputPeer*` types were
reviewed. Notably, `utils` is exempt on this because it needs
to deal with everything on a case-by-case basis.

Since the addition of `*FromMessage` peers, any manual `isinstance`
checks to determine the type were prone to breaking or being
forgotten to be updated, so a common `helpers._entity_type()`
method was made to share this logic.

Since the conversion to `Peer` would be too expensive, a simpler
check against the name is made, which should be fast and cheap.

telethon/client/messageparse.py

@@ -2,7 +2,7 @@ import itertools
 import re
 import typing
 
-from .. import utils
+from .. import helpers, utils
 from ..tl import types
 
 if typing.TYPE_CHECKING:
@@ -134,7 +134,7 @@ class MessageParseMethods:
                 id_to_message[update.message.id] = update.message
 
             elif (isinstance(update, types.UpdateEditMessage)
-                  and not isinstance(request.peer, types.InputPeerChannel)):
+                  and helpers._entity_type(request.peer) != helpers._EntityType.CHANNEL):
                 if request.id == update.message.id:
                     update.message._finish_init(self, entities, input_chat)
                     return update.message