Fixes#16602
This was broken when we refactored the members to use a single model for public channels. Those public channels then didn't have any members in their model they used for suggestions.
This is fixed by putting the logic in the UsersStore and reusing that store whenever we need a list of the members.
- simpler, standard property based API
- much lighter than deriving from the heavy StatusListItem
- should reduce RAM usage significantly, esp. with large communities
Iterates #11059
Jonathan Rainville
Lukáš Tinkl
Patryk Osmaczko
Sale Djenic