💡 Struct builder supporting inheritance

[amis92]

HaloFour wrote up an interesting solution for struct Builder that also supports inheritance and allows nice selective With update.

See https://gist.github.com/amis92/dfc52fb774d44194f8846b2f560c2f96

This would solve our following issues:

• A different kind of Wither: With(Optional...) A different kind of Wither: With(Optional...) #102
• PartialBuilder with Option properties as a "delta" PartialBuilder with Option properties as a "delta" #46
• Support positional/ordered and nominal/unordered data objects/records Support positional/ordered and nominal/unordered data objects/records #43
  struct Builder would nicely support unordered feature
• Enhance internal Builder workings Enhance internal Builder workings #41
• partially Support for record hierarchies Support for record hierarchies #12

@bboyle1234 @atifaziz @MKMZ request for comments :)

This could be a new "kind" of Record, mostly because it has a very different API. Maybe [NominalRecord] pointing to the fact it's nominal as in non-ordered/name-bound? Other ideas?

[amis92]

Gist taken from dotnet/csharplang#3174 (comment)