This fixes the user groups UI to follow the Zulip standard mechanisms
(using the appropriate server_events system to update all browsers
properly). It also, as a side effect, fixes#8692, since it
eliminates the weird behavior of trying to re-insert a user group
after reformatting it in the frontend.
Thanks to Tarun Kumar for preliminary work on this.
The main point of this change is to streamline the core
code for input pills, and we use also modify user groups.
The main change to input_pill.js is that you now
configure a function called `create_item_from_text`, and
that can return an arbitrary object, and it just needs
a field called `display_value`.
Other changes:
* You now call `input.create(opts)` to create the
widget.
* There is no longer a cache, because we can
write smarter code in typeahead `source` functions
that exclude ids up front.
* There is no value/optinalKey complexity, because
the calling code can supply arbitrary objects and
do their own external data management on the pill
items.
* We eliminate `prependPill`.
* We eliminate `data`, `keys`, and `values`, and just
have `items`.
This fixes the real-time sync for the user groups membership data
structure to work like these work in the rest of Zulip; now, edits
made in one browser are immediately and correctly reflected in other
browsers.
Tim Abbott
Steve Howell
Aditya Bansal
Cynthia Lin