Add PartialMessage to allow working with channel/message_id pairs.

Fix #5905

discord/channel.py

@@ -517,6 +517,28 @@ class TextChannel(discord.abc.Messageable, discord.abc.GuildChannel, Hashable):
         data = await self._state.http.follow_webhook(self.id, webhook_channel_id=destination.id, reason=reason)
         return Webhook._as_follower(data, channel=destination, user=self._state.user)
 
+    def get_partial_message(self, message_id):
+        """Creates a :class:`PartialMessage` from the message ID.
+
+        This is useful if you want to work with a message and only have its ID without
+        doing an unnecessary API call.
+
+        .. versionadded:: 1.6
+
+        Parameters
+        ------------
+        message_id: :class:`int`
+            The message ID to create a partial message for.
+
+        Returns
+        ---------
+        :class:`PartialMessage`
+            The partial message.
+        """
+
+        from .message import PartialMessage
+        return PartialMessage(channel=self, id=message_id)
+
 class VoiceChannel(discord.abc.Connectable, discord.abc.GuildChannel, Hashable):
     """Represents a Discord guild voice channel.