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)_.
if (reason === PasswordResponses.INCORRECT_PASSWORD) {
            throw new Error("Incorrect password");
          }
          
          expect(false).toEqual(true);
        };
        const result2 = passwordIncorrectLoadingTask.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.INCORRECT_PASSWORD);
            return passwordIncorrectLoadingTask.destroy();
          }
        );
        await Promise.all([result1, result2]);
      }
    );
    it("creates pdf doc from empty typed array", async function () {
      const loadingTask = getDocument(new Uint8Array(0));
      expect(loadingTask instanceof PDFDocumentLoadingTask).toEqual(true);
      try {
        await loadingTask.promise;
        
        expect(false).toEqual(true);
      
        expect(reason instanceof InvalidPDFException).toEqual(true);