[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>

src/gbm/gbtree.cc

@@ -135,7 +135,7 @@ void GBTree::PerformTreeMethodHeuristic(DMatrix* fmat) {
     return;
   }
 
-  if (rabit::IsDistributed()) {
+  if (collective::IsDistributed()) {
     LOG(INFO) << "Tree method is automatically selected to be 'approx' "
                  "for distributed training.";
     tparam_.tree_method = TreeMethod::kApprox;