Improve Legacy management in VTK
Following a discussion on VTK discourse, @ben.boeckel had a suggestion that could improve legacy management for VTK dependent software (ie ParaView). https://discourse.vtk.org/t/about-api-breaking-changes/1339/11
[...] fix VTK_LEGACY_REMOVE to work as a versioned check rather than be a global on/off switch. This would allow deprecations to be marked with VTK_LEGACY_API(8, 90, 0, 20190723) where ParaView could then set VTK_COMPAT_API=VTK_COMPAT_VERSION(8, 90, 0, 20190722) (or something) to say it is OK with API removals up until the 22nd and hides anything with a removal older than that and warns for anything deprecated since then.