Rename ThreadCurrentUserInfo to LegacyThreadCurrentUserInfo

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

For some reason we didn't rename ThreadCurrentUserInfo to LegacyThreadCurrentUserInfo previously. MinimallyEncodedThreadCurrentUserInfo will become the "new" ThreadCurrentUserInfo in subsequent diff.

Depends on D10791

Test Plan: flow

Reviewers: ashoat, ginsu, tomek

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D10792