[sledge] Add Map.max_binding

Reviewed By: ngorogiannis

Differential Revision: D27996950

fbshipit-source-id: b7a26c79d

sledge/nonstdlib/NSMap.ml

@@ -109,6 +109,7 @@ struct
   let choose = M.choose_opt
   let choose_exn = M.choose
   let min_binding = M.min_binding_opt
+  let max_binding = M.max_binding_opt
   let mem k m = M.mem k m
   let find_exn k m = M.find k m
   let find k m = M.find_opt k m

sledge/nonstdlib/NSMap_intf.ml

@@ -80,6 +80,7 @@ module type S = sig
       equivalent maps. [O(1)]. *)
 
   val min_binding : 'a t -> (key * 'a) option
+  val max_binding : 'a t -> (key * 'a) option
   val mem : key -> 'a t -> bool
   val find : key -> 'a t -> 'a option
   val find_exn : key -> 'a t -> 'a