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 passwordIncorrectLoadingTask = getDocument(
          buildGetDocumentParams(filename, {
            password: "qwerty",
          })
        );
        expect(
          passwordIncorrectLoadingTask instanceof PDFDocumentLoadingTask
        ).toEqual(true);
        let passwordNeededDestroyed;
        passwordNeededLoadingTask.onPassword = function (callback, reason) {
          if (reason === PasswordResponses.NEED_PASSWORD) {
            passwordNeededDestroyed = passwordNeededLoadingTask.destroy();
            return;
          }
          
          expect(false).toEqual(true);
        };
        const result1 = passwordNeededLoadingTask.promise.then(
          function () {
            
            expect(false).toEqual(true);
            return Promise.reject(new Error("loadingTask should be rejected"));
          
          function (reason) {
            expect(reason instanceof PasswordException).toEqual(true);
            expect(reason.code).toEqual(PasswordResponses.NEED_PASSWORD);
            return passwordNeededDestroyed;
          }
        );
        passwordIncorrectLoadingTask.onPassword = function (callback, reason) {