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)_.
});
    it("gets annotations containing relative URLs (bug 766086)", async function () {
      const filename = "bug766086.pdf";
      const defaultLoadingTask = getDocument(buildGetDocumentParams(filename));
      const defaultPromise = defaultLoadingTask.promise.then(function (pdfDoc) {
        return pdfDoc.getPage(1).then(function (pdfPage) {
          return pdfPage.getAnnotations();
        });
      });
      const docBaseUrlLoadingTask = getDocument(
        buildGetDocumentParams(filename, {
          docBaseUrl: "http://www.example.com/test/pdfs/qwerty.pdf",
        })
      );
      const docBaseUrlPromise = docBaseUrlLoadingTask.promise.then(function (
        pdfDoc
      ) {
        return pdfDoc.getPage(1).then(function (pdfPage) {
          return pdfPage.getAnnotations();
        });
      });
      const invalidDocBaseUrlLoadingTask = getDocument(
        buildGetDocumentParams(filename, {
          docBaseUrl: "qwerty.pdf",
        })
      );
      const invalidDocBaseUrlPromise =
        invalidDocBaseUrlLoadingTask.promise.then(function (pdfDoc) {
          return pdfDoc.getPage(1).then(function (pdfPage) {
            return pdfPage.getAnnotations();