[lib] Introduce member_ prefix for permission strings
Summary: This diff introduces the types for this new prefix, and updates parseThreadPermissionString to be able to parse it.
Test Plan:
The whole stack was tested as follows:
- Unit tests from D9686, which toggle user-surfaced permissions on and off and make sure no difference is caught. This ensures that the original issue introduced in D9686 isn't reintroduced
- Careful review of each descendant permission removed in D9686
- Create a community as userA and add userB. Grant tagging permissions to all members. Make sure userB can tag inside non-root channels
- Do above, then create a channel without userB, and make sure userB can't tag there either (or do anything other than view). This is the repro described here
- Do above, but also create a thread inside the channel (as userA) and make sure userB can't do anything inside the thread other than view, until they join the parent channel
Reviewers: tomek, inka
Reviewed By: tomek
Differential Revision: https://phab.comm.dev/D13013