Discussion on adlast.adl

[paul-thompson-helix]

Discussion edits on adlast.adl that exposes the names of primitives as union branches and also limits scope of TypeExpr type params to zero, one or many depending on case.

I think in terms of a short term route to connect different tooling it might be better instead to open the existing tooling to importing the existing adlast json instead of this half-old-half-new variant above.