[lib] Consume "new" ThreadInfo in lib/selectors

Summary:
Replace instances of LegacyThreadInfo | MinimallyEncodedThreadInfo with ThreadInfo in lib/selectors. Initially defered this because I ran into some flow issues, but it turned out I made a simple typo/mistake.

Depends on D10124

Test Plan: CI/flow/etc.

Reviewers: ashoat, ginsu, tomek, rohan

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D10125