[lib] Re-introduce RoleInfo ([Legacy/MinimallyEncoded]RoleInfo)

Summary:
Replace usages of LegacyRoleInfo | MinimallyEncodedRoleInfo with re-introduced RoleInfo.

This doesn't make much of a difference with RoleInfo since there are just a few occurrences, but has more of an impact on eg MinimallyEncodedThreadInfo

Depends on D10066

Test Plan: flow/CI/etc.

Reviewers: ashoat, ginsu, tomek, rohan

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D10068