Existential types are shown as $Any_'a in errors and hover #9068

Existential type variables of GADT constructors are shown with their internal name $Constructor_'a.

type rec any = Any('a): any

let get = (Any(x)) => x

This has type: $Any_'a
But it's expected to have type: 'a
The type constructor $Any_'a would escape its scope

Hover shows the same name:

type rec any = Any(array<'a>, 'a => string): any
let showAll = (Any(xs, f)) => xs->Array.map(f)
//                 ^ hover: array<$Any_'a>

The message could say that the type is existential, introduced by constructor Any, and that it can't leave the pattern match.