Following a sold-out run downtown, Jeremy O. Harris’ “Slave Play” is now on Broadway.  At once hysterical and alarming, this trenchant satire of white fragility, identity politics, racism, psychotherapy, and a certain brand of its crunchy practitioners is a conversation piece to top them all.  Thoughtfully written, constructed, and executed; thought-provoking, relevant, and a herald of what can be, “Slave Play” is a must-see of the season.