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("creates pdf doc from non-existent URL", async function () {
      if (!isNodeJS) {
        
        pending("Fails intermittently on Linux in browsers.");
      }
      const loadingTask = getDocument(
        buildGetDocumentParams("non-existent.pdf")
      );
      expect(loadingTask instanceof PDFDocumentLoadingTask).toEqual(true);
      try {
        await loadingTask.promise;
        
        expect(false).toEqual(true);
      
        expect(reason instanceof MissingPDFException).toEqual(true);
      }
      await loadingTask.destroy();
    });
    it("creates pdf doc from PDF file protected with user and owner password", async function () {
      const loadingTask = getDocument(buildGetDocumentParams("pr6531_1.pdf"));
      expect(loadingTask instanceof PDFDocumentLoadingTask).toEqual(true);
      const passwordNeededCapability = createPromiseCapability();
      const passwordIncorrectCapability = createPromiseCapability();
      
      
      loadingTask.onPassword = function (updatePassword, reason) {
        if (
          reason === PasswordResponses.NEED_PASSWORD &&
          !passwordNeededCapability.settled
        ) {