[PL] Extended source terms to 0D meshes

With that change "Volumetric"/"Python" source terms can be applied to nodes, as well.
Thereby, the special "Nodal" source term has become obsolete, now.

ProcessLib/BoundaryConditionAndSourceTerm/Python/Utils/CreateLocalAssemblers.h

@@ -33,10 +33,6 @@ void createLocalAssemblersPython(
     NumLib::IntegrationOrder const integration_order,
     ExtraCtorArgs&&... extra_ctor_args)
 {
-    static_assert(
-        GlobalDim == 1 || GlobalDim == 2 || GlobalDim == 3,
-        "Meshes with dimension greater than three are not supported.");
-
     using LocAsmFactory =
         LocalAssemblerFactoryPython<LocalAssemblerInterface,
                                     LocalAssemblerImplementation, GlobalDim,
@@ -82,6 +78,12 @@ void createLocalAssemblersPython(
 
     switch (dimension)
     {
+        case 0:
+            detail::createLocalAssemblersPython<0,
+                                                LocalAssemblerImplementation>(
+                dof_table, mesh_elements, local_assemblers, integration_order,
+                std::forward<ExtraCtorArgs>(extra_ctor_args)...);
+            break;
         case 1:
             detail::createLocalAssemblersPython<1,
                                                 LocalAssemblerImplementation>(

ProcessLib/BoundaryConditionAndSourceTerm/Python/Utils/NsAndWeight.h

@@ -91,13 +91,19 @@ struct NsAndWeight<ShapeFunction, ShapeFunction, ShapeMatrix, ShapeMatrix>
 
     Eigen::Ref<const Eigen::RowVectorXd> N(unsigned order) const
     {
-        if (order >= 2)
+        // For point elements shape functions are the same for all orders, so
+        // this specialization will be selected, which is OK for any shape
+        // function order for point elements.
+        if constexpr (!std::is_same_v<ShapeFunction, NumLib::ShapePoint1>)
         {
-            OGS_FATAL(
-                "Only shape functions of order < 2 are available in the "
-                "current setting. You have requested order {}. Maybe there is "
-                "an error in the OGS project file.",
-                order);
+            if (order >= 2)
+            {
+                OGS_FATAL(
+                    "Only shape functions of order < 2 are available in the "
+                    "current setting. You have requested order {}. Maybe there "
+                    "is an error in the OGS project file.",
+                    order);
+            }
         }
 
         return N_;

ProcessLib/BoundaryConditionAndSourceTerm/Utils/CreateLocalAssemblers.h

@@ -33,10 +33,6 @@ void createLocalAssemblers(
     NumLib::IntegrationOrder const integration_order,
     ExtraCtorArgs&&... extra_ctor_args)
 {
-    static_assert(
-        GlobalDim == 1 || GlobalDim == 2 || GlobalDim == 3,
-        "Meshes with dimension greater than three are not supported.");
-
     using LocalAssemblerFactory =
         LocalAssemblerFactory<LocalAssemblerInterface,
                               LocalAssemblerImplementation, GlobalDim,
@@ -83,6 +79,12 @@ void createLocalAssemblers(
 
     switch (dimension)
     {
+        case 0:
+            detail::createLocalAssemblers<0, LocalAssemblerImplementation>(
+                dof_table, shapefunction_order, mesh_elements, local_assemblers,
+                integration_order,
+                std::forward<ExtraCtorArgs>(extra_ctor_args)...);
+            break;
         case 1:
             detail::createLocalAssemblers<1, LocalAssemblerImplementation>(
                 dof_table, shapefunction_order, mesh_elements, local_assemblers,