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)_.
comb: false,
            editable: true,
            hidden: false,
            name: "Text1",
            rect: [24.1789, 719.66, 432.22, 741.66],
            actions: null,
            page: 0,
            strokeColor: null,
            fillColor: null,
            type: "text",
          
        ],
        Button1: [
          {
            id: "26R",
            value: "Off",
            defaultValue: null,
            exportValues: undefined,
            editable: true,
            name: "Button1",
            rect: [455.436, 719.678, 527.436, 739.678],
            hidden: false,
            actions: {
              Action: [
                `this.getField("Text1").value = this.info.authors.join("::");`,
              ],
            
            page: 0,
            strokeColor: null,
            fillColor: new Uint8ClampedArray([192, 192, 192]),