[lib] Remove most remaining instances of LegacyThreadInfo from codebase

Summary:
Part of https://linear.app/comm/issue/ENG-6366/rename-minimallyencodedrawthreadinfo-to-rawthreadinfo

Will handle threadInfoFromRawThreadInfo and type utilities (conversion + validators) in subsequent diff for easier review.

Depends on D10713

Test Plan: flow

Reviewers: ashoat, ginsu, tomek

Reviewed By: ginsu

Differential Revision: https://phab.comm.dev/D10715