[lib] Introduce minimallyEncodeRawThreadInfo(RawThreadInfo): MinimallyEncodedRawThreadInfo

Summary:
Handy utility function that will make encoding/decoding of permissions/role permissions much simpler at callsite and avoid polluting with a bunch of permission encoding related stuff in eg rawThreadInfosFromServerThreadInfos.

Depends on D9736

Test Plan: Single unit test for now, will add more after decode function is introduced.

Reviewers: ashoat, ginsu, tomek, rohan

Reviewed By: tomek

Subscribers: wyilio

Differential Revision: https://phab.comm.dev/D9737