Draft: VTK: update for nlohmannjson header usage
This fixes the superbuild's compilations.
- Ben Boeckel: json-fwd-decls (vtk/vtk!11223 (merged))
- Jaswant Panchumarti: speed-up-quick-stage (vtk/vtk!11219 (merged))
GitLab update will be applied on June 28th, between 8am and 10:30am, EDT (UTC-04:00). This site may have intermittent delays during that time.
This fixes the superbuild's compilations.