Item field is added to the pill items, this is done to utilize
it wherever possible, to distinguish between diffrent types
of pill items(stream|user_groups|users).
It is also a preparatory commit to support expanding of stream
and user group pills.
This extra commit adds support for creating user group pills
in cases that do not use typeahead like, pasting the group
name, copying it from the user group pill.
This completes the remaining work required to support
addition of all members of a user groups to stream.
Fixes#15186.
We update the pills typeahead logic to also include user group
results and pass the "user_group" key in `opts` to enable this
option for Add subscriber form.
The changes includes:
* Exporting the `query_matches_name_description` function, to
deduplicate the typeahead `matcher` logic.
* Creating a `people.is_known_user` function, to deduplicate
the typeahead `sorter` logic.
* Add a new `user_group_pill.js`, to allow adding user group
pills in input widgets that support pills.
This has been tested manually as well as by adding some new
node tests.
m-e-l-u-h-a-n