[lib] Narrow ClientFullStateSync to MinimallyEncodedRawThreadInfos

Summary:
Similar to D10606 and D10608, this will allow us to remove invariant from D10588.

Depends on D10608

Test Plan: NA, flow

Reviewers: ashoat, ginsu, tomek

Reviewed By: ashoat

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10609