extensions/references-view/src/types/model.ts/TypesModel/_resolveTypes
class TypesModel:	private async _resolveTypes(currentType: TypeItem): Promise<TypeItem[]> {
		if (this.direction === TypeHierarchyDirection.Supertypes) {
			const types = await vscode.commands.executeCommand<vscode.TypeHierarchyItem[]>('vscode.provideSupertypes', currentType.item);
			return types ? types.map(item => new TypeItem(this, item, currentType)) : [];
		} else {
			const types = await vscode.commands.executeCommand<vscode.TypeHierarchyItem[]>('vscode.provideSubtypes', currentType.item);
			return types ? types.map(item => new TypeItem(this, item, currentType)) : [];
		}
	}