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)_.
const loant(
        buildGetDocumentParams("poppler-85140-0.pdf")
      );
      expect(loadingTask1 instanceof PDFDocumentLoadingTask).toEqual(true);
      expect(loadingTask2 instanceof PDFDocumentLoadingTask).toEqual(true);
      const pdfDocument1 = await loadingTask1.promise;
      const pdfDocument2 = await loadingTask2.promise;
      expect(pdfDocument1.numPages).toEqual(1);
      expect(pdfDocument2.numPages).toEqual(1);
      const page = await pdfDocument1.getPage(1);
      expect(page instanceof PDFPageProxy).toEqual(true);
      const opList = await page.getOperatorList();
      expect(opList.fnArray.length).toBeGreaterThan(5);
      expect(opList.argsArray.length).toBeGreaterThan(5);
      expect(opList.lastChunk).toEqual(true);
      try {
        await pdfDocument2.getPage(1);
        
        expect(false).toEqual(true);
      
        expect(reason instanceof UnknownErrorException).toEqual(true);
        expect(reason.message).toEqual("Bad (uncompressed) XRef entry: 3R");
      }
      await Promise.all([loadingTask1.destroy(), loadingTask2.destroy()]);
    });
    it("creates pdf doc from PDF files, with circular references", async function () {
      const loadingTask1 = getDocument(
        buildGetDocumentParams("poppler-91414-0-53.pdf")
      );
      const loant(