One of the most anticipated films of this awards season, “Ma Rainey’s Black Bottom” emerges as one of the premier Oscar vehicles for Netflix. At its soulful core, the farewell performance of the late Chadwick Boseman is as invigorating as anticipated. His work as Levee may very well be his best and most spiritual gift to cinema. Boseman has a real opportunity to join a short list that includes Peter Finch and Heath Ledger, two posthumous Oscar nominees who won their respective categories.