[lib] Introduce patchRawThreadInfosWithSpecialRole()

Summary: This will be used as part of native migration to add specialRole field to RoleInfos. This function is (RawThreadInfos) => RawThreadInfos which we can pass to updateClientDBThreadStoreThreadInfos as the migrationFunc.

Test Plan: Unit tests. Want to test this behavior outside of the running app so it was easier to ensure correct behavior w/ debugger:

Reviewers: ginsu, tomek

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D11056