[lib] Introduce patchRoleInfoWithSpecialRole(RoleInfo): RoleInfo

Summary:
This utility function will be consumed by native and web migration to set the specialRole field for existing threads in the thread store.

Created separate diffs and unit tests for this function so I could test in lightweight way before testing migration which is more heavy weight

Test Plan: Unit tests

Reviewers: tomek, ginsu

Reviewed By: ginsu

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D11055