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(statEntryThree.name).toEqual("Overall");
      expect(statEntryThree.end - statEntryThree.start).toBeGreaterThan(0);
      CanvasFactory.destroy(canvasAndCtx);
      await loadingTask.destroy();
    });
    it("cancels rendering of page", async function () {
      const viewport = page.getViewport({ scale: 1 });
      const canvasAndCtx = CanvasFactory.create(
        viewport.width,
        viewport.height
      );
      const renderTask = page.render({
        canvasContext: canvasAndCtx.context,
        canvasFactory: CanvasFactory,
        viewport,
      });
      expect(renderTask instanceof RenderTask).toEqual(true);
      renderTask.cancel();
      try {
        await renderTask.promise;
        
        expect(false).toEqual(true);
      
        expect(reason instanceof RenderingCancelledException).toEqual(true);
        expect(reason.message).toEqual("Rendering cancelled, page 1");
        expect(reason.type).toEqual("canvas");
      }
      CanvasFactory.destroy(canvasAndCtx);
    });
    it("re-render page, using the same canvas, after cancelling rendering", async function () {