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 
actionDict.set("URI", "www.hmrc.gov.uk");
        const annotationDict = new Dict();
        annotationDict.set("Type", Name.get("Annot"));
        annotationDict.set("Subtype", Name.get("Link"));
        annotationDict.set("A", actionDict);
        const annotationRef = Ref.get(353, 0);
        const xref = new XRefMock([
          { ref: annotationRef, data: annotationDict },
        ]);
        AnnotationFactory.create(
          xref,
          annotationRef,
          pdfManagerMock,
          idFactoryMock
        ).then(({ data }) => {
          expect(data.annotationType).toEqual(AnnotationType.LINK);
          expect(data.url).toEqual("http://www.hmrc.gov.uk/");
          expect(data.unsafeUrl).toEqual("http://www.hmrc.gov.uk");
          expect(data.dest).toBeUndefined();
          done();
        }, done.fail);
      }
    );
    it(
      "should correctly parse a URI action, where the URI entry " +
        "has an incorrect encoding (bug 1122280)",
      function (done) {
        const actionStream = new StringStream(
          "<<\n" +
            "/Type /Action\n" +