add test for completions crash

tests/cases/fourslash/completionsWrappedClass.ts

@@ -0,0 +1,18 @@
+/// <reference path="fourslash.ts" />
+
+////class Client {
+////    private close() { }
+////    public open() { }
+////}
+////type Wrap<T> = T &
+////{
+////    [K in Extract<keyof T, string> as `${K}Wrapped`]: T[K];
+////};
+////class Service {
+////    method() {
+////        let service = undefined as unknown as Wrap<Client>;
+////        const { /*a*/ } = service;
+////    }
+////}
+
+verify.completions({ marker: "a", exact: ["open", "openWrapped"] });