This extends the /json/typing endpoint to also accept
stream_id and topic. With this change, the requests
sent to /json/typing should have these:
* `to`: a list set to
- recipients for a PM
- stream_id for a stream message
* `topic`, in case of stream message
along with `op`(start or stop).
On receiving a request with stream_id and topic, we send
typing events to clients with stream_typing_notifications set
to True for all users subscribed to that stream.
api docs filenames are basically the operationId of their endpoint
in zulip.yaml with `_` replaced by `-`. But some operationIds have
changed, so change the affected filenames. Make changes in other
files accordingly.