[lib] Update useResolvedThreadInfosObj return type

Summary: One of the changes from https://gist.github.com/Ashoat/efa03bb380aa602abe2499770b9ddfbd. Separating into separate diff because the other change caused some cascading flow issues in native... which I'll address in separate diff.

Test Plan: flow

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D9935