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 
dict.set("Type", Name.get("Annot"));
      dict.set("Subtype", Name.get("Text"));
      const xref = new XRefMock([{ ref, data: dict }]);
      AnnotationFactory.create(xref, ref, pdfManagerMock, idFactoryMock).then(
        ({ data }) => {
          expect(data.inReplyTo).toBeUndefined();
          expect(data.replyType).toBeUndefined();
          done();
        },
        done.fail
      );
    });
    it("should parse IRT and set default RT when not defined.", function (done) {
      const annotationRef = Ref.get(819, 0);
      const annotationDict = new Dict();
      annotationDict.set("Type", Name.get("Annot"));
      annotationDict.set("Subtype", Name.get("Text"));
      const replyRef = Ref.get(820, 0);
      const replyDict = new Dict();
      replyDict.set("Type", Name.get("Annot"));
      replyDict.set("Subtype", Name.get("Text"));
      replyDict.set("IRT", annotationRef);
      const xref = new XRefMock([
        { ref: annotationRef, data: annotationDict },
        { ref: replyRef, data: replyDict },
      ]);
      annotationDict.assignXref(xref);
      replyDict.assignXref(xref);
      AnnotationFactory.create(
        xref,