Classes that implement WinRTPromiseBase do not declare the "extra" promise-like functions

[dunhor]

E.g. this results in the error:

windows/WinRTTurboModule/Generated Files/types/Windows.Storage.Streams.d.ts:46:11 - error TS2420: Class 'DataReaderLoadOperation' incorrectly implements interface 'WinRTPromiseBase<number, void> & Promise<number>'.
  Type 'DataReaderLoadOperation' is not assignable to type 'WinRTPromiseBase<number, void>'.
    Type 'DataReaderLoadOperation' is missing the following properties from type 'WinRTPromiseBase<number, void>': then, done, operation

46     class DataReaderLoadOperation implements Windows.Foundation.WinRTPromise<number, void>, Windows.Foundation.IAsyncInfo {
             ~~~~~~~~~~~~~~~~~~~~~~~