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 pdfDoc = await loadingTask.promise;
      const pdfPage = await pdfDoc.getPage(1);
      const operatorList = await pdfPage.getOperatorList();
      const imgIndex = operatorList.fnArray.indexOf(OPS.paintImageXObject);
      const imgArgs = operatorList.argsArray[imgIndex];
      const { data } = pdfPage.objs.get(imgArgs[0]);
      expect(data instanceof Uint8ClampedArray).toEqual(true);
      expect(data.length).toEqual(90000);
      await loadingTask.destroy();
    });
    it(
      "gets operatorList, from corrupt PDF file (issue 8702), " +
        "with/without `stopAtErrors` set",
      async function () {
        const loadingTask1 = getDocument(
          buildGetDocumentParams("issue8702.pdf", {
            stopAtErrors: false, // The default value.
          })
        );
        const loant(
          buildGetDocumentParams("issue8702.pdf", {
            stopAtErrors: true,
          })
        );
        const result1 = loadingTask1.promise.then(pdfDoc => {
          return pdfDoc.getPage(1).then(pdfPage => {
            return pdfPage.getOperatorList().then(opList => {
              expect(opList.fnArray.length).toBeGreaterThan(100);
              expect(opList.argsArray.length).toBeGreaterThan(100);
              expect(opList.lastChunk).toEqual(true);