Bound the size of the histogram cache. (#9440)

- A new histogram collection with a limit in size.
- Unify histogram building logic between hist, multi-hist, and approx.

tests/cpp/test_learner.cc

@@ -92,7 +92,7 @@ TEST(Learner, CheckGroup) {
 
   std::shared_ptr<DMatrix> p_mat{RandomDataGenerator{kNumRows, kNumCols, 0.0f}.GenerateDMatrix()};
   std::vector<bst_float> weight(kNumGroups, 1);
-  std::vector<bst_int> group(kNumGroups);
+  std::vector<bst_group_t> group(kNumGroups);
   group[0] = 2;
   group[1] = 3;
   group[2] = 7;