This commit renames "huddle" to "direct_message_group" in the
web codebase. It also renames the file - "huddle_data.ts" to
"direct_message_group_data.ts"
Fixes part of #28640
Reproducer:
* Have some unreads in the Combined feed view.
* Scroll up and select a message that was not part of initial fetch.
* Reload.
* Go a another narrow.
* Come back to combined feed to find your at a random message. This
message is actually last message of the current fetch of
combined feed view which was returned via `first_unread_message_id`.
This is no longer required since narrow state is restored by
`reload` library and narrow history restores the narrow pointer
and offset when going back to a view.
Only regression here is we will no longer restore the pointer when
user navigates to the combined feed view without using browser back
button and combined feed view is the default view. This is fixed
in the next commit.