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)_.
});
  });
  describe("PDFDataRangeTransport", function () {
    let dataPromise;
    beforeAll(function () {
      const fileName = "tracemonkey.pdf";
      dataPromise = DefaultFileReaderFactory.fetch({
        path: TEST_PDFS_PATH + fileName,
      });
    });
    afterAll(function () {
      dataPromise = null;
    });
    it("should fetch document info and page using ranges", async function () {
      const initialDataLength = 4000;
      let fetches = 0;
      const data = await dataPromise;
      const initialData = data.subarray(0, initialDataLength);
      const transport = new PDFDataRangeTransport(data.length, initialData);
      transport.reque (begin, end) {
        fetches++;
        waitSome(function () {
          transport.onDataProgress(4000);
          transport.onDataRange(begin, data.subarray(begin, end));
        });
      };
      const loadingTask = getDocument(transport);
      const pdfDocument = await loadingTask.promise;
      expect(pdfDocument.numPages).toEqual(14);
      const pdfPage = await pdfDocument.getPage(10);