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)_.
await testCanLoad("basicapi.pdf?cors=withCredentials", {
          withCredentials: false,
        });
      });
    });
  });
  describe("Page", function () {
    let pdfLoadingTask, pdfDocument, page;
    beforeAll(async function () {
      pdfLoadingTask = getDocument(basicApiGetDocumentParams);
      pdfDocument = await pdfLoadingTask.promise;
      page = await pdfDocument.getPage(1);
    });
    afterAll(async function () {
      await pdfLoadingTask.destroy();
    });
    it("gets page number", function () {
      expect(page.pageNumber).toEqual(1);
    });
    it("gets rotate", function () {
      expect(page.rotate).toEqual(0);
    });
    it("gets ref", function () {
      expect(page.ref).toEqual({ num: 15, gen: 0 });
    });
    it("gets userUnit", function () {