[lib] Expand ThreadInfo to LegacyThreadInfo | MinimallyEncodedThreadInfo in thread-utils

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

Similarly to D10640, initially had issues with this file so decided to address in separate diff from D10639. However, it looks like I must've made some mistake initially because there are no longer any flow issues.

Depends on D10640

Test Plan: flow

Reviewers: ashoat, ginsu, tomek

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D10641