Ast.ScopeDefSourceInside a scope, a definition can refer either to a scope def, or a subscope def
type t = | Var of Shared_ast.ScopeVar.t * Shared_ast.StateName.t option| SubScopeVar of Shared_ast.SubScopeName.t
* Shared_ast.ScopeVar.t
* Catala_utils.Pos.t