src/vs/workbench/contrib/typeHierarchy/common/typeHierarchy.ts/TypeHierarchyModel/constructor
class TypeHierarchyModel:	fork(item: TypeHierarchyItem): TypeHierarchyModel {
		const that = this;
		return new class extends TypeHierarchyModel {
			constructor() {
				super(that.id, that.provider, [item], that.ref.acquire());
			}
		};
	}