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

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

Previously had issues with this file as part of D10639 and decided to address in separate diff to avoid making that diff hard to review. However, looks like I must've made some sort of mistake initially because there are no longer any flow issues.

Depends on D10639

Test Plan: flow

Reviewers: ashoat, ginsu, tomek

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D10640