Building ParaView on opensuse leap 15.0 fails due to qhelpgenerator

The normal ParaView macros search for qhelpgenerator manually, not with the cmake components and thus don't find qhelpgenerator-qt5 like it is installed as in leap-15.0

• Discussion: https://discourse.paraview.org/t/building-paraview-5-5-2-on-opensuse-leap-15-0
• Bug report: https://gitlab.kitware.com/paraview/paraview/issues/18317
• Solution: https://gitlab.kitware.com/paraview/paraview/merge_requests/2608