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 pageLayout = await pdfDoc.getPageLayout();
      expect(pageLayout).toEqual("");
      await loadingTask.destroy();
    });
    it("gets non-default page layout", async function () {
      const pageLayout = await pdfDocument.getPageLayout();
      expect(pageLayout).toEqual("SinglePage");
    });
    it("gets default page mode", async function () {
      const loadingTask = getDocument(
        buildGetDocumentParams("tracemonkey.pdf")
      );
      const pdfDoc = await loadingTask.promise;
      const pageMode = await pdfDoc.getPageMode();
      expect(pageMode).toEqual("UseNone");
      await loadingTask.destroy();
    });
    it("gets non-default page mode", async function () {
      const pageMode = await pdfDocument.getPageMode();
      expect(pageMode).toEqual("UseOutlines");
    });
    it("gets default viewer preferences", async function () {
      const loadingTask = getDocument(
        buildGetDocumentParams("tracemonkey.pdf")
      );
      const pdfDoc = await loadingTask.promise;
      const prefs = await pdfDoc.getViewerPreferences();
      expect(prefs).toEqual(null);
      await loadingTask.destroy();
    });