ENH: support VTK output of uniform field

src/conversion/vtk/output/foamVtkInternalWriter.H

src/conversion/vtk/output/foamVtkInternalWriterTemplates.C

src/conversion/vtk/output/foamVtkPatchWriter.H

src/conversion/vtk/output/foamVtkPatchWriterTemplates.C

src/fileFormats/vtk/file/foamVtkFileWriter.H

src/fileFormats/vtk/file/foamVtkFileWriterTemplates.C

src/fileFormats/vtk/write/foamVtkSurfaceWriter.H

src/fileFormats/vtk/write/foamVtkSurfaceWriterTemplates.C

src/meshTools/output/foamVtkIndPatchWriter.H

src/meshTools/output/foamVtkIndPatchWriterTemplates.C