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)_.
return loadingTask1.destroy();
            });
          });
        });
        const result2 = loadingTask2.promise.then(pdfDoc => {
          return pdfDoc.getPage(1).then(pdfPage => {
            return pdfPage.getOperatorList().then(opList => {
              expect(opList.fnArray.length).toEqual(0);
              expect(opList.argsArray.length).toEqual(0);
              expect(opList.lastChunk).toEqual(true);
              return loadingTask2.destroy();
            });
          });
        });
        await Promise.all([result1, result2]);
      }
    );
    it("gets operator list, containing Annotation-operatorLists", async function () {
      const loadingTask = getDocument(
        buildGetDocumentParams("annotation-line.pdf")
      );
      const pdfDoc = await loadingTask.promise;
      const pdfPage = await pdfDoc.getPage(1);
      const operatorList = await pdfPage.getOperatorList();
      expect(operatorList.fnArray.length).toBeGreaterThan(20);
      expect(operatorList.argsArray.length).toBeGreaterThan(20);
      expect(operatorList.lastChunk).toEqual(true);
      // The `getOperatorList` method, similar to the `render` method,
      // is supposed to include any existing Annotation-operatorLists.
      expect(operatorList.fnArray.includes(OPS.beginAnnotation)).toEqual(true);