[lib] Update roleIsAdminRole to consider roleInfo?.specialRole

Summary:
Update the roleIsAdminRole utility to consider roleInfo?.specialRole field when handling clients where specialRole has been populated.

Note that this branch will be skipped because specialRole field is not yet set on clients.

Test Plan:

1. Hard code includeSpecialRoleFieldInRoles to true
2. Check to see that specialRole field of roles are populated in ThreadStore
3. Set a breakpoint and see that the branch is hit and function behaves as expected.

Reviewers: ginsu, tomek, kamil, michal

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D11148