[lib] Narrow types in memberHasAdminPowers call stack to remove invariant

Summary:
Narrow types from innerThreadFrozenDueToBlock down to memberHasAdminPowers, removing ThreadInfo and RelativeMemberInfo such that we can remove the invariant introduced in D12265.

We're now good with removing permissions field from ThreadInfo, now we just need to remove it from RawThreadInfo and we can proceed to migration and toggling shape of RawThreadInfo on keyserver based on codeVersion checks.

There's some tidying up to do eg removing skipMemberAdminRoleCheck and pulling out logic common to threadIsWithBlockedUserOnly and threadIsWithBlockedUserOnlyWithoutAdminRoleCheck, but will handle those in followup diffs for convenience.

Depends on D12290

Test Plan: just flow.

Reviewers: ashoat, ginsu, tomek, varun

Reviewed By: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12292