Put isForum in ChatTypeSupergroup chat

[Fra078]

It would be useful to check if a chat is a forum directly without request to a cache with supergroup IDs to improve performance when loading lists

[levlam]

is_forum can be changed any time, so it isn't part of the chat's type. It can be added only with the updateChatType update, which sounds a bit strange.

While it is true that this looks like the only reason to fetch the supergroup object from cache while showing chat list, I don't think that the change will result in any reasonable performance improvements.

[Fredmattwg]

Hi