[native] Barebones user selection in CommunityCreationMembers

Summary:
Extremely barebones user selection screen in CommunityCreationMembers using TagInput and UserList.

There's a warning about nested scroll views, the styling isn't correct, and we aren't differentiating between COMMUNITY_ROOT and COMMUNITY_ANNOUNCEMENT_ROOT. Going to handle each of those in followup diffs to keep changes easier to review.

Test Plan:
Works as expected:

Reviewers: ashoat, ginsu

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D8056