[native][web] Navigate to a thread if already joined
Summary:
When a user already joined a thread or a community, check the most specific chat (a thread is more specific than its community because the fact that a user is a member of a thread requires the user to be a member of this thread's community) and navigate to it if appropriate.
Depends on D12399
Test Plan:
Tested on both native and web. Used a link to a thread and to a community where the viewer was a member and verified that a thread or a community was opened.
Also checked if the text in a modal correctly reflects whether it is a community or a thread link.
Reviewers: inka, ginsu, kamil
Reviewed By: kamil
Subscribers: ashoat
Differential Revision: https://phab.comm.dev/D12420