[web] Remove instances of LegacyThreadInfo throughout web
Summary:
Part of https://linear.app/comm/issue/ENG-6366/rename-minimallyencodedrawthreadinfo-to-rawthreadinfo
This diff addresses the flow issues that arose in web as a consequence of D10670. There are more instances of LegacyThreadInfo/LegacyResolvedThreadInfo in subsequent diffs.
[skip-ci]
Depends on D10670
Test Plan: flow
Reviewers: ashoat, ginsu, tomek
Reviewed By: ashoat
Differential Revision: https://phab.comm.dev/D10671