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.url).toEqual("https://developer.mozilla.org/en-US/");
        done();
      }, done.fail);
    });
    it("should handle URL in AA dict in push buttons", function (done) {
      const buttonWidgetRef = Ref.get(124, 0);
      buttonWidgetDict.set("Ff", AnnotationFieldFlag.PUSHBUTTON);
      // D stands for MouseDown
      const dDict = new Dict();
      dDict.set("S", Name.get("JavaScript"));
      dDict.set(
        "JS",
        "app.launchURL('https://developer.mozilla.org/en-US/', true)"
      );
      const actionDict = new Dict();
      actionDict.set("D", dDict);
      buttonWidgetDict.set("AA", actionDict);
      const xref = new XRefMock([
        { ref: buttonWidgetRef, data: buttonWidgetDict },
      ]);
      AnnotationFactory.create(
        xref,
        buttonWidgetRef,
        pdfManagerMock,