In the following spots a "MouseUp" eventName is being used, which does look inconsistent considering that the "Mouse Down"/"Mouse Enter"/"Mouse Exit" eventNames all have a space in them.
Is this inconsistency actually expected, or is it a simple typo? If the former, then a comment explaining *why* would be appropriate; otherwise we should just fix this :-)

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L806

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L945

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L1034

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L1168

/cc @calixteman 
oldData.data = oldData.data.replace(/\(D:[0-9]+\)/, "(date)");
          expect(oldData.data).toEqual(
            "123 0 obj\n" +
              "<< /Type /Annot /Subtype /Widget /FT /Tx /DA (/Goth 5 Tf) /DR " +
              "<< /Font << /Helv 314 0 R /Goth 159 0 R>>>> /Rect [0 0 32 10] " +
              `/V (\xfe\xff${utf16String}) /AP << /N 2 0 R>> /M (date)>>\nendobj\n`
          );
          expect(newData.data).toEqual(
            "2 0 obj\n<< /Length 82 /Subtype /Form /Resources " +
              "<< /Font << /Helv 314 0 R /Goth 159 0 R>>>> /BBox [0 0 32 10]>> stream\n" +
              `/Tx BMC q BT /Goth 5 Tf 1 0 0 1 0 0 Tm 2.00 2.00 Td (${utf16String}) Tj ` +
              "ET Q EMC\nendstream\nendobj\n"
          );
          done();
        }, done.fail);
    });
  });
  describe("ButtonWidgetAnnotation", function () {
    let buttonWidgetDict;
    beforeEach(function (done) {
      buttonWidgetDict = new Dict();
      buttonWidgetDict.set("Type", Name.get("Annot"));
      buttonWidgetDict.set("Subtype", Name.get("Widget"));
      buttonWidgetDict.set("FT", Name.get("Btn"));
      done();
    });
    afterEach(function () {
      buttonWidgetDict = null;
    });
    it("should handle checkboxes with exrt value", function (done) {