Polymorphic Hugrs (values)

[acl-cqc]

Will need to bind some typeparams in the Hugr (or possibly some wrapper thereof that can be stored in e.g. a Const)

[acl-cqc]

Thinking a bit more about where TypeParams should be declared.

For a Module-level Hugr, it probably makes sense for each FuncDefn (or FuncDecl) to declare it's own TypeParams. Possibly each AliasDecl/Defn too?? But less likely each Const.

So, we could include a list of TypeParams in each of those OpTypes. This probably works for Hugrs rooted at any of those OpTypes and also for Module (i.e. there are no module-level params).

However, we'll also want TypeParams for any Hugr that is rooted at a Dfg or Cfg node (these express anonymous, non-recursive, functions, rather than named FuncDecls...right???). However, it doesn't make sense to declare TypeParams for a Dfg node that's nested within another Dfg (only one that's within a Const, or a "free Hugr" as we have many of in tests).

[acl-cqc]

This was largely done by #692 with remainder pushed out to #708 and #709