[MeL/Elements] Make getNodeIndex a free function.

Applications/FileIO/FEFLOW/FEFLOWMeshInterface.cpp

Applications/FileIO/SWMM/SWMMInterface.cpp

Applications/FileIO/TetGenInterface.cpp

Applications/Utils/ModelPreparation/PartitionMesh/Metis.cpp

MeshGeoToolsLib/BoundaryElementsAlongPolyline.cpp

MeshGeoToolsLib/BoundaryElementsOnSurface.cpp

MeshGeoToolsLib/IdentifySubdomainMesh.cpp

MeshLib/Elements/Element.cpp

MeshLib/Elements/Element.h

MeshLib/Elements/TemplateElement-impl.h

MeshLib/Elements/TemplateElement.h

MeshLib/Mesh.cpp

MeshLib/MeshEditing/RemoveMeshComponents.cpp

MeshLib/MeshGenerators/LayeredVolume.cpp

MeshLib/MeshGenerators/MeshLayerMapper.cpp

MeshLib/MeshGenerators/QuadraticMeshGenerator.cpp

MeshLib/MeshGenerators/RasterToMesh.cpp

MeshLib/MeshSearch/NodeSearch.cpp

MeshLib/convertMeshToGeo.cpp

NumLib/Function/Interpolation.h