Use realloc for histogram cache and expose the cache limit. (#9455)

doc/parameter.rst

@@ -226,6 +226,15 @@ Parameters for Tree Booster
     - ``one_output_per_tree``: One model for each target.
     - ``multi_output_tree``:  Use multi-target trees.
 
+* ``max_cached_hist_node``, [default = 65536]
+
+  Maximum number of cached nodes for CPU histogram.
+
+  .. versionadded:: 2.0.0
+
+  - For most of the cases this parameter should not be set except for growing deep trees
+    on CPU.
+
 .. _cat-param:
 
 Parameters for Categorical Feature