[lib/web/native] Display community role for users in subchannels/sidebars

Summary:
Currently, the members modal will display the correct role for community roots (i.e. 'Members', 'Admins'), but will only display 'Members' for subchannels/sidebars. This is because of the way that ThreadInfo only contains the Members role for these threads.

The solution here is to introspect into the community's threadInfo for that specific thread, and pull the roles from there for each member. This will ensure that we have access to all of the community roles.

I noted in a code comment, but the special case is for GENESIS, where we don't readily have access to the community's members (and also roles are not really supported there), so in that case we'll just read the current ThreadInfo for the role (probably 'Members' for subchannels/sidebars).

Resolves https://linear.app/comm/issue/ENG-5178/ashoat-shows-up-under-admins-column-but-with-members-pill

Test Plan:
Please see the test videos below (also tested for custom roles)

Before Web:
Before Native:

After Web:
After Native:

Reviewers: atul, ginsu, ashoat

Reviewed By: ashoat

Subscribers: ted, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9430