Proposal: Remove records in variants

[jfmengels]

For most variants of the different types defined in this package, we use separate elements. For instance, for if we have Expression.If (Node Expression) (Node Expression) (Node Expression), and I think this works quite well even if they're not named.

But for a few of our variants, we use records hidden behind aliases: (I'll use the Nonempty notation from #192)

Expression.LambdaExpression Lambda, where Lambda = { arguments : NonEmpty (Node DestructurePattern), expression : Node Expression }. We could instead have Expression.Lambda (NonEmpty (Node DestructurePattern)) (Node Expression). Removing the definition for Lambda will also allow to rename LambdaExpression to Lambda.

Expression.Case CaseBlock, where CaseBlock = { expression : Node Expression, cases : NonEmpty Case }. We could instead have Expression.Case (Node Expression) (NonEmpty Case). Case is defined as ( Node Pattern, Node Expression ), and I would actually like to remove it too as I find it more confusing than helpful. That would lead us to Expression.Case (Node Expression) (NonEmpty ( Node Pattern, Node Expression ))

Expression.Let LetBlock, where LetBlock = { declarations : NonEmpty (Node LetDeclaration), expression : Node Expression }. We could instead have `Expression.Let (NonEmpty (Node LetDeclaration)) (Node Expression). (TODO this one hasn't been turned into a non empty list yet, create an issue)

If we do flatten everything, then it might make sense to inline RecordSetter for Record and RecordUpdate.

I don't know if we should apply this logic to other types, I haven't looked at those yet.

[miniBill]

YES please. Those are so much better for pattern matching