[lib] implement checking if user supports thick thread

Summary:
ENG-9394

Depends on D13488

Test Plan:
Search for users and check on the icon:

Made sure that users which have Local DM are registered to Identity, other users are either reserved usernames or only from my local keyserver

Reviewers: ashoat, tomek

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D13489