Add patch to build with VTK 9.1

François Mazenrequested to merge
mzf/itksnap:fix_vtk9_build into master

Current version of the package does not build due to changes in VTK 9.1.

This Merge Request patches the file GUI/Renderer/IntensityCurveVTKRenderer.cxx by adding the missing header and updating with the new API.

@tille @gladk

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