Merge changes from topic 'notedb-comments-map'

* changes:
  Move getCommentPsId from notedb to common location
  Fix PatchLineCommentsUtil.draftByChangeAuthor
  Convert CommentJson to more of a builder style
  Rename List(Draft)Comments to ListRevision{Drafts,Comments}
  notedb: Rewrite comments to be keyed by RevId
  Rename PatchLineCommentComparator to PLC_ORDER
  Convert ChangeNotes tests to Truth
  Convert CommentsTest to Truth
  Add RevId.toString()