Thread local memory allocation for BuildHist (#6358)

* thread mem locality

* fix apply

* cleanup

* fix lint

* fix tests

* simple try

* fix

* fix

* apply comments

* fix comments

* fix

* apply simple comment

Co-authored-by: ShvetsKS <kirill.shvets@intel.com>

tests/cpp/common/test_partition_builder.cc

@@ -32,6 +32,8 @@ TEST(PartitionBuilder, BasicTest) {
     for(size_t j = 0; j < tasks[nid]; ++j) {
       size_t begin = kBlockSize*j;
       size_t end = kBlockSize*(j+1);
+      const size_t id = builder.GetTaskIdx(nid, begin);
+      builder.AllocateForTask(id);
 
       auto left  = builder.GetLeftBuffer(nid, begin, end);
       auto right = builder.GetRightBuffer(nid, begin, end);