[MaL/LinAlg] Generalize the linear solver option parsing.

MathLib/LinAlg/LinearSolverOptionsParser.h

+/**
+ * \file
+ * \copyright
+ * Copyright (c) 2012-2021, OpenGeoSys Community (http://www.opengeosys.org)
+ *            Distributed under a Modified BSD License.
+ *              See accompanying file LICENSE.txt or
+ *              http://www.opengeosys.org/project/license
+ *
+ */
+
+#pragma once
+
+namespace MathLib
+{
+template <typename LinearSolverType>
+struct LinearSolverOptionsParser;
+}  // namespace MathLib