Name of default export should not appear in import completion lists #6124

Named default exports don't export a named declaration with the original name, so we shouldn't show that name in the list.

• `file1.ts

  export var x = 10;
  
  export default class C {
  
  }

• file2.ts

  import { /**/ } from "./file1";

Request completion at /**/

Expected: x and default^[1] appears in list
Actual: x and C appear in list.

^[1] Yes, default is valid; an ImportSpecifier can have an IdentifierName on the left of the as keyword. As a refresher, an IdentifierName has no restrictions on it.