Fix for the userCallback type - error and user positions were reversed.

[princefishthrower]

As the title states, I noticed the type signature for userCallback is incorrect - namely, the order of user and error are reversed. This is of course a pain in that TypeScript complains because it thinks the user object is an error object, for example in the callbacks to sendbird.connect or sendbird.updateCurrentUserInfo. This pull request would resolve that typing issue.

[princefishthrower]

Actually, nearly all of the callback signatures (just found another with groupChannelListQueryCallback, and many others) have this type reversal issue, and is making TypeScript typing errors very annoying in our code. Either the shape of what is returned has to be fixed, or all the typings have to be.

I'm hoping such a widespread typing issue can be resolved quickly - it would greatly improve our development efforts with sendbird.

[alminmemmo]

Same issue with getTotalUnreadChannelCount, version 3.1.7