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 attachment = attachments["foo.txt"];
      expect(attachment.filename).toEqual("foo.txt");
      expect(attachment.content).toEqual(
        new Uint8Array([98, 97, 114, 32, 98, 97, 122, 32, 10])
      );
      await loadingTask.destroy();
    });
    it("gets javascript", async function () {
      const javascript = await pdfDocument.getJavaScript();
      expect(javascript).toEqual(null);
    });
    it("gets javascript with printing instructions (JS action)", async function () {
      
      const loadingTask = getDocument(buildGetDocumentParams("issue6106.pdf"));
      const pdfDoc = await loadingTask.promise;
      const javascript = await pdfDoc.getJavaScript();
      expect(javascript).toEqual([
        "this.print({bUI:true,bSilent:false,bShrinkToFit:true});",
      ]);
      expect(javascript[0]).toMatch(AutoPrintRegExp);
      await loadingTask.destroy();
    });
    it("gets hasJSActions, in document without javaScript", async function () {
      const hasJSActions = await pdfDocument.hasJSActions();
      expect(hasJSActions).toEqual(false);
    });
    it("gets hasJSActions, in document with javaScript", async function () {
      const loadingTask = getDocument(
        buildGetDocumentParams("doc_actions.pdf")
      );