Cleanup: Move five mesh related files to C++

To faciliate further mesh data structure refactoring. See #103343.

Pull Request #105354

source/blender/python/mathutils/mathutils.h

@@ -10,6 +10,10 @@
 
 #include "BLI_compiler_attrs.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 struct DynStr;
 
 extern char BaseMathObject_is_wrapped_doc[];
@@ -228,3 +232,7 @@ int column_vector_multiplication(float r_vec[4], VectorObject *vec, MatrixObject
 /* dynstr as python string utility functions, frees 'ds'! */
 PyObject *mathutils_dynstr_to_py(struct DynStr *ds);
 #endif
+
+#ifdef __cplusplus
+}
+#endif