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)_.
it("gets metadata, with corrupt /Metadata XRef entry", async function () {
      const loadingTask = getDocument(
        buildGetDocumentParams("PDFBOX-3148-2-fuzzed.pdf")
      );
      const pdfDoc = await loadingTask.promise;
      const { info, metadata, contentDispositionFilename, contentLength } =
        await pdfDoc.getMetadata();
      
      expect(info.Custom).toEqual(undefined);
      
      expect(info.PDFFormatVersion).toEqual("1.6");
      expect(info.Language).toEqual(null);
      expect(info.EncryptFilterName).toEqual(null);
      expect(info.IsLinearized).toEqual(false);
      expect(info.IsAcroFormPresent).toEqual(true);
      expect(info.IsXFAPresent).toEqual(false);
      expect(info.IsCollectionPresent).toEqual(false);
      expect(info.IsSignaturesPresent).toEqual(false);
      expect(metadata).toEqual(null);
      expect(contentDispositionFilename).toEqual(null);
      expect(contentLength).toEqual(244351);
      await loadingTask.destroy();
    });
    it("gets markInfo", async function () {
      const loadingTask = getDocument(
        buildGetDocumentParams("annotation-line.pdf")
      );
      const pdfDoc = await loadingTask.promise;
      const markInfo = await pdfDoc.getMarkInfo();
      expect(markInfo.Marked).toEqual(true);