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 
widgetDict.set("Type", Name.get("Annot"));
      widgetDict.set("Subtype", Name.get("Widget"));
      done();
    });
    afterEach(function () {
      widgetDict = null;
    });
    it("should handle unknown field names", function (done) {
      const widgetRef = Ref.get(20, 0);
      const xref = new XRefMock([{ ref: widgetRef, data: widgetDict }]);
      AnnotationFactory.create(
        xref,
        widgetRef,
        pdfManagerMock,
        idFactoryMock
      ).then(({ data }) => {
        expect(data.annotationType).toEqual(AnnotationType.WIDGET);
        expect(data.fieldName).toEqual("");
        done();
      }, done.fail);
    });
    it("should construct the field name when there are no ancestors", function (done) {
      widgetDict.set("T", "foo");
      const widgetRef = Ref.get(21, 0);
      const xref = new XRefMock([{ ref: widgetRef, data: widgetDict }]);
      AnnotationFactory.create(
        xref,
        widgetRef,
        pdfManagerMock,
        idFactoryMock