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(outlineItem.italic).toEqual(false);
      expect(outlineItem.color).toEqual(new Uint8ClampedArray([0, 64, 128]));
      expect(outlineItem.items.length).toEqual(1);
      expect(outlineItem.items[0].title).toEqual("Paragraph 1.1");
    });
    it("gets outline containing a URL", async function () {
      const loadingTask = getDocument(buildGetDocumentParams("issue3214.pdf"));
      const pdfDoc = await loadingTask.promise;
      const outline = await pdfDoc.getOutline();
      expect(Array.isArray(outline)).toEqual(true);
      expect(outline.length).toEqual(5);
      const outlineItemTwo = outline[2];
      expect(typeof outlineItemTwo.title).toEqual("string");
      expect(outlineItemTwo.dest).toEqual(null);
      expect(outlineItemTwo.url).toEqual("http://google.com/");
      expect(outlineItemTwo.unsafeUrl).toEqual("http://google.com");
      expect(outlineItemTwo.newWindow).toBeUndefined();
      const outlineItemOne = outline[1];
      expect(outlineItemOne.bold).toEqual(false);
      expect(outlineItemOne.italic).toEqual(true);
      expect(outlineItemOne.color).toEqual(new Uint8ClampedArray([0, 0, 0]));
      await loadingTask.destroy();
    });
    it("gets outline with non-displayable chars", async function () {
      const loadingTask = getDocument(buildGetDocumentParams("issue14267.pdf"));
      const pdfDoc = await loadingTask.promise;
      const outline = await pdfDoc.getOutline();
      expect(Array.isArray(outline)).toEqual(true);
      expect(outline.length).toEqual(1);
      const outlineItem = outline[0];