TsTypeUnion only works in top level export

[halsandr]

I am finding that the [TsTypeUnions] attribute only works when it is in an interface that has [ExportTsInterface], if it is on a dependant type, then the union is ignored.

---

Controller.cs

    [ExportTsInterface]
    public interface TestController
    {
        TestUnion ControllerProp { get; set; }
    }

    public interface TestUnion
    {
        [TsTypeUnions("number")]
        string TestUnionProp { get; set; }
    }

TestUnion.d.ts

export interface TestUnion {
    TestUnionProp: string;
}

---

Controller.cs

    [ExportTsInterface]
    public interface TestUnion
    {
        [TsTypeUnions("number")]
        string TestUnionProp { get; set; }
    }

TestUnion.d.ts

export interface TestUnion {
    TestUnionProp: string | number;
}