[lib] Remove most remaining instances of LegacyThreadInfo from lib
Summary:
Part of https://linear.app/comm/issue/ENG-6366/rename-minimallyencodedrawthreadinfo-to-rawthreadinfo
NOTE: There are some remaining instances in lib related to message specs and in thread-utils that'll be handled in subsequent diffs for (maybe) easier review.
Depends on D10676
Test Plan: flow
Reviewers: ashoat, ginsu, tomek
Reviewed By: tomek
Differential Revision: https://phab.comm.dev/D10677