Add test case for nested namespace

tests/cases/fourslash/importNameCodeFixNewImportFile4.ts

@@ -0,0 +1,16 @@
+/// <reference path="fourslash.ts" />
+
+//// [|let t: A/*0*/.B.I;|]
+
+// @Filename: ./module.ts
+//// export namespace A {
+////    export namespace B {
+////        export interface I { }
+////    }
+//// }
+
+verify.importFixAtPosition([
+`import { A } from "./module";
+
+let t: A.B.I;`
+]);