[Redesign] Update Inline Comment UI

Summary: Ref T8099, Simplifies the button bar with a borderless option and implements in Differential Inline Commenting.

Test Plan:
Review new and old comments, submitted, unsubmitted, ghosts, done.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T8099

Differential Revision: https://secure.phabricator.com/D13475