[web] Add a selector fetching thread IDs according to COMMUNITIES calendar filter

Summary:
issue: https://linear.app/comm/issue/ENG-2794/make-it-possible-to-display-only-chats-from-a-given-community-in-the
Since D6645 the calendar filters reducer reacts to updateCalendarCommunityFilter and clearCalendarCommunityFilter actions. We want to be able to extract the thread IDs based on the filters these actions have set.

Test Plan:
Dispatch updateCalendarCommunityFilter and clearCalendarCommunityFilter actions, log the value returned by filteredCommunityThreadIDsSelector. Check that it is correct. Check that it is only
possible to add an event for a chat in the selected community (in the web app) - this is a result of updating onScreenThreadInfos that is used by ThreadPickerModal

Reviewers: kamil, tomek

Reviewed By: kamil, tomek

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D6461