Hello!

Let me know if i should have opened this issue on the [pdfjs-dist](https://github.com/mozilla/pdfjs-dist) repo but I though here would fit.

I'm using pdfjs-dist and I'm in need of some more types to be exported. I have no idea how the types end up in the dist-repo but would love to open a PR if only someone could point me in the right direction 😃 Since I was using an older version of pdfjs-dist I realize the only type I need that's not in the type defs in the latest release are _PageViewport_ from _[display/display_utils](https://github.com/mozilla/pdf.js/blob/master/src/display/display_utils.js#L153)_.
expect(
        passwordNeededLoadingTask instanceof PDFDocumentLoadingTask
      ).toEqual(true);
      const result1 = passwordNeededLoadingTask.promise.then(
        function () {
          
          expect(false).toEqual(true);
          return Promise.reject(new Error("loadingTask should be rejected"));
        
        function (data) {
          expect(data instanceof PasswordException).toEqual(true);
          expect(data.code).toEqual(PasswordResponses.NEED_PASSWORD);
          return passwordNeededLoadingTask.destroy();
        }
      );
      const passwordIncorrectLoadingTask = getDocument(
        buildGetDocumentParams(filename, {
          password: "qwerty",
        })
      );
      expect(
        passwordIncorrectLoadingTask instanceof PDFDocumentLoadingTask
      ).toEqual(true);
      const result2 = passwordIncorrectLoadingTask.promise.then(
        function () {
          
          expect(false).toEqual(true);
          return Promise.reject(new Error("loadingTask should be rejected"));
        
        function (data) {