move remaining vectors, boxes in chalk-ir into associated types on `Interner`

[nikomatsakis]

In general, we have been trying to remove hard-coded vectors and boxes from the chalk-ir APIs, and moving them instead to Interner associated types. See the chalk book for more background on the Interner trait and its design.

This issue tracks the removal of the final vectors etc:

• Vec<ProgramClause<I>> in Environment -- introduce ProgramClauses -- done in Intern Vec<ProgramClause<I>> #370
• Vec<QuantifiedWhereClause<I>> in DyTy -- introduce QuantifiedWhereClauses -- done in Intern Vec<QuantifiedWhereClause<I>>. #379
• Vec<Parameter> in Fn (this should be changed to Substitution) -- done in extend chalk TypeName with builtin types #368
• Vec<ParameterKind<()>> in Binders, BindersIntoIterator -- introduce ParameterKinds -- Migrate Vec<ParameterKinds<()>> and Vec<ParameterKinds<UniverseIndex>> to interned #386
• Vec<ParameterKind<Universe>> in Canonical -- hmm, this one requires a bit of thought, because I think we want to reconcile other bits of canonicalization -- Migrate Vec<ParameterKinds<()>> and Vec<ParameterKinds<UniverseIndex>> to interned #386

Here are some example PRs showing how this removal can be done:

• intern "substitutions" #316 converted a Vec<Parameter> into the Substitution<I> type
• Goals and folding goals #325 replaced Vec<Goal<I>> with Goals<I>

This issue has been assigned to @crlf0710 via this comment.

[crlf0710]

Will have a try this weekend.

[crlf0710]

Edit: Seems #370 is in flight.

[nikomatsakis]

@crlf0710 there are still other issues to claim -- e.g., QuantifiedWhereClauses, ParameterKinds, etc. Feel free to claim one of those.

[crlf0710]

Changed Vec<Parameter> to Substitution in Fn in #378.

I'll have a try on Vec<QuantifiedWhereClause<I>> next.

[crlf0710]

Introduced QuantifiedWhereClauses in #379.

[crlf0710]

Given the rest a try in #386

[crlf0710]

@rustbot claim