[CL] Get chemical system index map.

ChemistryLib/ChemicalSolverInterface.h

@@ -29,5 +29,8 @@ public:
     }
 
     virtual ~ChemicalSolverInterface() = default;
+
+public:
+    std::vector<std::vector<GlobalIndexType>> chemical_system_index_map;
 };
 }  // namespace ChemistryLib