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(page3Actions).toEqual({
        PageOpen: [`this.getField("Text5").value = "PageOpen 3";`],
        PageClose: [`this.getField("Text6").value = "PageClose 3";`],
      });
      await loadingTask.destroy();
    });
    it("gets non-existent fieldObjects", async function () {
      const fieldObjects = await pdfDocument.getFieldObjects();
      expect(fieldObjects).toEqual(null);
    });
    it("gets fieldObjects", async function () {
      if (isNodeJS) {
        pending(
          "Node.js appears to ignore Object properties that are explicitly " +
            "set to `undefined`, thus breaking the expectations used below."
        );
      }
      const loadingTask = getDocument(buildGetDocumentParams("js-authors.pdf"));
      const pdfDoc = await loadingTask.promise;
      const fieldObjects = await pdfDoc.getFieldObjects();
      expect(fieldObjects).toEqual({
        Text1: [
          {
            id: "25R",
            value: "",
            defaultValue: null,
            multiline: false,
            password: false,
            charLimit: null,