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 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);
      }
      const reRenderTask = page.render({
        canvasContext: canvasAndCtx.context,
        canvasFactory: CanvasFactory,
        viewport,
      });
      expect(reRenderTask instanceof RenderTask).toEqual(true);
      await reRenderTask.promise;
      CanvasFactory.destroy(canvasAndCtx);
    });
    it("multiple render() on the same canvas", async function () {
      const optionalContentConfigPromise =