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)_.
children: [
                  {
                    role: "NonStruct",
                    children: [{ type: "content", id: "page2R_mcid2" }],
                  
                ],
              
              {
                role: "P",
                children: [
                  {
                    role: "NonStruct",
                    children: [{ type: "content", id: "page2R_mcid3" }],
                  
                ],
              
            ],
          
        ],
      });
      await loadingTask.destroy();
    });
    it("gets operator list", async function () {
      const operatorList = await page.getOperatorList();
      expect(operatorList.fnArray.length).toBeGreaterThan(100);
      expect(operatorList.argsArray.length).toBeGreaterThan(100);
      expect(operatorList.lastChunk).toEqual(true);
    });
    it("gets operatorList with JPEG image (issue 4888)", async function () {
      const loadingTask = getDocument(buildGetDocumentParams("cmykjpeg.pdf"));