Place IMesh interface in its own file

src/mesh/GmshReader.hpp

@@ -5,7 +5,7 @@
 
 #include <utils/Array.hpp>
 
-#include <mesh/Mesh.hpp>
+#include <mesh/IMesh.hpp>
 #include <mesh/RefId.hpp>
 
 #include <array>

src/mesh/IMesh.hpp

+#ifndef I_MESH_HPP
+#define I_MESH_HPP
+
+#include <cstddef>
+
+struct IMesh
+{
+ public:
+  virtual size_t dimension() const = 0;
+
+  IMesh(const IMesh&) = delete;
+  IMesh(IMesh&&)      = delete;
+
+  IMesh()  = default;
+  ~IMesh() = default;
+};
+
+#endif   // I_MESH_HPP

src/mesh/Mesh.hpp

@@ -2,24 +2,12 @@
 #define MESH_HPP
 
 #include <algebra/TinyVector.hpp>
-
+#include <mesh/IMesh.hpp>
 #include <mesh/ItemValue.hpp>
 #include <utils/CSRGraph.hpp>
 
 #include <memory>
 
-struct IMesh
-{
- public:
-  virtual size_t dimension() const = 0;
-
-  IMesh(const IMesh&) = delete;
-  IMesh(IMesh&&)      = delete;
-
-  IMesh()  = default;
-  ~IMesh() = default;
-};
-
 template <typename ConnectivityType>
 class Mesh final : public IMesh
 {