[Breaking] Switch from rabit to the collective communicator (#8257)

* Switch from rabit to the collective communicator

* fix size_t specialization

* really fix size_t

* try again

* add include

* more include

* fix lint errors

* remove rabit includes

* fix pylint error

* return dict from communicator context

* fix communicator shutdown

* fix dask test

* reset communicator mocklist

* fix distributed tests

* do not save device communicator

* fix jvm gpu tests

* add python test for federated communicator

* Update gputreeshap submodule

Co-authored-by: Hyunsu Philip Cho <chohyu01@cs.washington.edu>

jvm-packages/xgboost4j-flink/src/main/scala/ml/dmlc/xgboost4j/scala/flink/XGBoost.scala

@@ -19,7 +19,7 @@ package ml.dmlc.xgboost4j.scala.flink
 import scala.collection.JavaConverters.asScalaIteratorConverter
 
 import ml.dmlc.xgboost4j.LabeledPoint
-import ml.dmlc.xgboost4j.java.{Rabit, RabitTracker}
+import ml.dmlc.xgboost4j.java.{Communicator, RabitTracker}
 import ml.dmlc.xgboost4j.scala.{DMatrix, XGBoost => XGBoostScala}
 
 import org.apache.commons.logging.LogFactory
@@ -46,7 +46,7 @@ object XGBoost {
                      collector: Collector[XGBoostModel]): Unit = {
       workerEnvs.put("DMLC_TASK_ID", String.valueOf(this.getRuntimeContext.getIndexOfThisSubtask))
       logger.info("start with env" + workerEnvs.toString)
-      Rabit.init(workerEnvs)
+      Communicator.init(workerEnvs)
       val mapper = (x: LabeledVector) => {
         val (index, value) = x.vector.toSeq.unzip
         LabeledPoint(x.label.toFloat, x.vector.size, index.toArray, value.map(_.toFloat).toArray)
@@ -59,7 +59,7 @@ object XGBoost {
           .map(_.toString.toInt).getOrElse(0)
       val booster = XGBoostScala.train(trainMat, paramMap, round, watches,
         earlyStoppingRound = numEarlyStoppingRounds)
-      Rabit.shutdown()
+      Communicator.shutdown()
       collector.collect(new XGBoostModel(booster))
     }
   }