MM-34758 Collapsed Reply Threads without mobile support (#17424)

Summary
added support for legacy clients accessing server
added collapsed_threads_supported param to viewChannel API and setPostUnread API

Ticket Link
https://mattermost.atlassian.net/browse/MM-34758

Related Webapp PR
mattermost/mattermost-webapp#7933

store/store.go

@@ -216,7 +216,7 @@ type ChannelStore interface {
 	PermanentDeleteMembersByUser(userID string) error
 	PermanentDeleteMembersByChannel(channelID string) error
 	UpdateLastViewedAt(channelIds []string, userID string, updateThreads bool) (map[string]int64, error)
-	UpdateLastViewedAtPost(unreadPost *model.Post, userID string, mentionCount, mentionCountRoot int, updateThreads bool) (*model.ChannelUnreadAt, error)
+	UpdateLastViewedAtPost(unreadPost *model.Post, userID string, mentionCount, mentionCountRoot int, updateThreads bool, setUnreadCountRoot bool) (*model.ChannelUnreadAt, error)
 	CountPostsAfter(channelID string, timestamp int64, userID string) (int, int, error)
 	IncrementMentionCount(channelID string, userID string, updateThreads, isRoot bool) error
 	AnalyticsTypeCount(teamID string, channelType string) (int64, error)
@@ -288,6 +288,7 @@ type ThreadStore interface {
 	GetPosts(threadID string, since int64) ([]*model.Post, error)
 
 	MarkAllAsRead(userID, teamID string) error
+	MarkAllAsReadInChannels(userID string, channelIDs []string) error
 	MarkAsRead(userID, threadID string, timestamp int64) error
 
 	SaveMembership(membership *model.ThreadMembership) (*model.ThreadMembership, error)