[lib] Update threadInfoFromRawThreadInfo to return MinimallyEncodedThreadInfo

Summary: Update threadInfoFromRawThreadInfo to always return MinimallyEncodedThreadInfo and update eg baseCreatePendingSidebar to accomodate that. Now all newly created pending threads on the client will be MinimallyEncoded.. so "new threads" going into Redux will be MinimallyEncoded and we won't be creating legacyThreadInfos on the client.

Test Plan: CI/flow/etc.

Reviewers: ashoat, ginsu, tomek, rohan

Reviewed By: rohan

Differential Revision: https://phab.comm.dev/D10195