Add LivestreamChannelController (#3750)

* 1st WIP

* Handle more mapping

* Make message list diff kit to support updating from Array instead of LazyCollection

* Handle events in LivestreamChannelController

* fixup message list view

* Add reads and attachments

* Forward live stream events and don't save them into the DB

* Use currentUserId and channel from DB for now (Maybe implement caching later)

* Simplify model mapping

* Fix current user reactions

* Improve how event notification center knows when to do manually event handling

* Do WIP on reads

* Remove reads since it is not needed for live streams

* Add DemoLivestreamChannelVC to the DemoApp

* Remove unread stuff from LivestreamChannelController

* Add ChatLivestreamChannelVC to be able to test

* Handle message errors

* Fix regular controller not working after showing as livestream

* Fix sometimes messages disappearing from the view

* Quick jumps fix for Live Stream

* Fix some minor typos

* Move Payload to asModel() to seperate files

* Handling new messages while first page is not loaded

* Remove atomics

* Add API only message actions to the livestream controller

- deleteMessages
- loadReactins
- flag
- unflag
- addReaction
- deleteReaction
- pin
- unpin

* Add createNewMessage to `LivestreamChannelController`

* Remove markRead from livestream controller

* Load initial page from cache

* Add reaction groups and moderation details to Message Payload model mapping

* If event is not handled, fallback to middlewares

* Add Combine support for livestream controller

* Handle channel update events and make it easier to notify delegates

* Cache local channels when handling manual events

* Fix not loading older pages when in skip logic

* Add slow mode support to Livestream Controller

* Extract manual event handling logic to a ManualEventHandler

* Fix merge conflict

* CodeRabit review feedback changes

* Cleanuo livestream channel controller

* Cleanup model mapping

* Move livestream UI to the demo app

* Quick fix typo

* Handle pagination with willDisplayAt

* Log a warning instead of a error when a feature is disabled

* Do not use channel controller in the composer

* Fix message actions on livestream demo UI

* Fix minor warning

* Add  support for setting max number of messages in livestream controller

* Add a way to check how much messages were skipped when the controller was paused

* Add `isPause` publisher

* Disable the discarding of messages by default

* Reset the live stream channel controller when memory warning is received

* Fix attachments not working

* Explicitly disable commands

* Fix access control of livestream channel view

* Use reactions from livestream controller in the demo app livestream UI

* Display list of reaction authors when tapping the reactions in the message list

* Change the thread to utility in the Manual Event Handler

* Do not copy the current message everytime when doing in-memory message updates

* Improve doc of livestream channel controller message capping

* Print whenever the livestream messages are updated

* Only count skipped messages if enabled

* Make the completion blocks and delegates as main actors

* Fix loadReactions completion not in the MainActor

* Fix thread-safeness when fetching cached channel in manual event handler

* Remove cooldown protections

* Fix creating a new message not resuming the controller

* Save the channel to the DB on the first page fetch

* Remove unnecessary isBounce in live reactions view

* Add loadPinnedMessage to livestream controller

* Handle channel updates through the DB

* Update CHANGELOG.md

* Fix existing tests

* Remove ChannelDetailPayload as model since it is not used

* Fix tests related to pending messages

* Add test coverage to user payload model conversion

* Add test coverage to message payload model conversion

* Add test coverage to channel payload model conversion

* Add missing tests to disable slow mode

* Add test coverage to LivestreamChannelController

* Fix UI Tests not compiling

* Add combine test coverage

* Add memory warning test coverage

* Add missing test coverage to the event notification centre

* Add test coverage to ManualEventHandler

Author: nuno-vieira

CHANGELOG.md

@@ -6,6 +6,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ## StreamChat
 ### ✅ Added
 - Add pending messages support [#3754](https://github.com/GetStream/stream-chat-swift/pull/3754)
+- Add new lightweight `LivestreamChannelController` that improves performance for live chats [#3750](https://github.com/GetStream/stream-chat-swift/pull/3750)
 ### 🐞 Fixed
 - Fix `ChatClient.currentUserId` not removed instantly after calling `logout()` [#3766](https://github.com/GetStream/stream-chat-swift/pull/3766)