We want to introduce a specialRole field to the RoleInfo/LegacyRoleInfo type so we can include it when fetching threads/roles, and going forward perform checks on role.specialRole instead of relying on role.isDefault since this won't extend to checking for other special roles (like Admins).
This diff introduces this field as specialRole?: ?number to prevent flow errors. Towards the end of this stack, I plan to change this type to specialRole: ?number so we always include specialRole, whether it is a number or null.
Part of ENG-5994
Even though, there are currently no uses of InfoBlock we don't want to completely remove the component since the plan is to repurpose the component in a subsequent diff