reworked includes in source files (#2066)

* added all necessary includes - fixed build/include_what_you_use error

* fixed the order of includes (build/include_order)

src/treelearner/gpu_tree_learner.h

 #ifndef LIGHTGBM_TREELEARNER_GPU_TREE_LEARNER_H_
 #define LIGHTGBM_TREELEARNER_GPU_TREE_LEARNER_H_
 
-#include <LightGBM/utils/random.h>
-#include <LightGBM/utils/array_args.h>
 #include <LightGBM/dataset.h>
-#include <LightGBM/tree.h>
 #include <LightGBM/feature_group.h>
-#include "feature_histogram.hpp"
-#include "serial_tree_learner.h"
-#include "data_partition.hpp"
-#include "split_info.hpp"
-#include "leaf_splits.hpp"
+#include <LightGBM/tree.h>
+#include <LightGBM/utils/array_args.h>
+#include <LightGBM/utils/random.h>
 
-#include <cstdio>
-#include <vector>
-#include <random>
+#include <string>
 #include <cmath>
+#include <cstdio>
 #include <memory>
+#include <random>
+#include <vector>
+
+#include "data_partition.hpp"
+#include "feature_histogram.hpp"
+#include "leaf_splits.hpp"
+#include "serial_tree_learner.h"
+#include "split_info.hpp"
 
 #ifdef USE_GPU
 

src/treelearner/leaf_splits.hpp

 #ifndef LIGHTGBM_TREELEARNER_LEAF_SPLITS_HPP_
 #define LIGHTGBM_TREELEARNER_LEAF_SPLITS_HPP_
 
-#include <limits>
-
 #include <LightGBM/meta.h>
-#include "data_partition.hpp"
 
+#include <limits>
 #include <vector>
 
+#include "data_partition.hpp"
+
 namespace LightGBM {
 
 /*!

src/treelearner/parallel_tree_learner.h

 #ifndef LIGHTGBM_TREELEARNER_PARALLEL_TREE_LEARNER_H_
 #define LIGHTGBM_TREELEARNER_PARALLEL_TREE_LEARNER_H_
 
-#include "serial_tree_learner.h"
-#include "gpu_tree_learner.h"
 #include <LightGBM/network.h>
-
 #include <LightGBM/utils/array_args.h>
 
 #include <cstring>
-#include <vector>
 #include <memory>
+#include <vector>
+
+#include "gpu_tree_learner.h"
+#include "serial_tree_learner.h"
 
 namespace LightGBM {
 

src/treelearner/serial_tree_learner.cpp

@@ -2,13 +2,13 @@
 
 #include <LightGBM/network.h>
 #include <LightGBM/objective_function.h>
-
 #include <LightGBM/utils/array_args.h>
 #include <LightGBM/utils/common.h>
 
 #include <algorithm>
-#include <vector>
 #include <queue>
+#include <unordered_map>
+#include <utility>
 
 namespace LightGBM {
 

src/treelearner/serial_tree_learner.h

 #ifndef LIGHTGBM_TREELEARNER_SERIAL_TREE_LEARNER_H_
 #define LIGHTGBM_TREELEARNER_SERIAL_TREE_LEARNER_H_
-#include <LightGBM/tree_learner.h>
-
-#include <LightGBM/utils/random.h>
-#include <LightGBM/utils/array_args.h>
 
 #include <LightGBM/dataset.h>
 #include <LightGBM/tree.h>
+#include <LightGBM/tree_learner.h>
+#include <LightGBM/utils/array_args.h>
+#include <LightGBM/utils/random.h>
+
+#include <string>
+#include <cmath>
+#include <cstdio>
+#include <memory>
+#include <random>
+#include <vector>
 
-#include "feature_histogram.hpp"
-#include "split_info.hpp"
 #include "data_partition.hpp"
+#include "feature_histogram.hpp"
 #include "leaf_splits.hpp"
+#include "split_info.hpp"
 
-#include <cstdio>
-#include <vector>
-#include <random>
-#include <cmath>
-#include <memory>
 #ifdef USE_GPU
 // Use 4KBytes aligned allocator for ordered gradients and ordered hessians when GPU is enabled.
 // This is necessary to pin the two arrays in memory and make transferring faster.

src/treelearner/split_info.hpp

@@ -3,11 +3,12 @@
 
 #include <LightGBM/meta.h>
 
+#include <limits>
 #include <cmath>
 #include <cstdint>
 #include <cstring>
-#include <limits>
 #include <functional>
+#include <vector>
 
 namespace LightGBM {
 

src/treelearner/tree_learner.cpp

 #include <LightGBM/tree_learner.h>
 
-#include "serial_tree_learner.h"
 #include "gpu_tree_learner.h"
 #include "parallel_tree_learner.h"
+#include "serial_tree_learner.h"
 
 namespace LightGBM {
 

src/treelearner/voting_parallel_tree_learner.cpp

-#include "parallel_tree_learner.h"
-
 #include <LightGBM/utils/common.h>
 
 #include <cstring>
 #include <tuple>
 #include <vector>
 
+#include "parallel_tree_learner.h"
+
 namespace LightGBM {
 
 template <typename TREELEARNER_T>