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 
AnnotationFactory.create(
        xref,
        buttonWidgetRef,
        pdfManagerMock,
        idFactoryMock
      ).then(({ data }) => {
        expect(data.annotationType).toEqual(AnnotationType.WIDGET);
        expect(data.checkBox).toEqual(true);
        expect(data.fieldValue).toEqual("1");
        expect(data.defaultFieldValue).toEqual("2");
        expect(data.radioButton).toEqual(false);
        expect(data.exrtValue).toEqual("Checked");
        done();
      }, done.fail);
    });
    it("should render checkbox with fallback font for printing", function (done) {
      const appearanceStatesDict = new Dict();
      const normalAppearanceDict = new Dict();
      const checkedAppearanceDict = new Dict();
      const uncheckedAppearanceDict = new Dict();
      const checkedStream = new StringStream("/ 12 Tf (4) Tj");
      checkedStream.dict = checkedAppearanceDict;
      const uncheckedStream = new StringStream("");
      uncheckedStream.dict = uncheckedAppearanceDict;
      checkedAppearanceDict.set("BBox", [0, 0, 8, 8]);
      checkedAppearanceDict.set("FormType", 1);
      checkedAppearanceDict.set("Matrix", [1, 0, 0, 1, 0, 0]);
      normalAppearanceDict.set("Checked", checkedStream);
      normalAppearanceDict.set("Off", uncheckedStream);
      appearanceStatesDict.set("N", normalAppearanceDict);