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 
fileSpecDict.set("Desc", "");
      fileSpecDict.set("EF", embeddedFileDict);
      fileSpecDict.set("UF", "Test.txt");
      const fileAttachmentRef = Ref.get(20, 0);
      const fileAttachmentDict = new Dict();
      fileAttachmentDict.set("Type", Name.get("Annot"));
      fileAttachmentDict.set("Subtype", Name.get("FileAttachment"));
      fileAttachmentDict.set("FS", fileSpecRef);
      fileAttachmentDict.set("T", "Topic");
      fileAttachmentDict.set("Contents", "Test.txt");
      const xref = new XRefMock([
        { ref: fileStreamRef, data: fileStreamDict },
        { ref: fileSpecRef, data: fileSpecDict },
        { ref: fileAttachmentRef, data: fileAttachmentDict },
      ]);
      embeddedFileDict.assignXref(xref);
      fileSpecDict.assignXref(xref);
      fileAttachmentDict.assignXref(xref);
      AnnotationFactory.create(
        xref,
        fileAttachmentRef,
        pdfManagerMock,
        idFactoryMock
      ).then(({ data }) => {
        expect(data.annotationType).toEqual(AnnotationType.FILEATTACHMENT);
        expect(data.file.filename).toEqual("Test.txt");
        expect(data.file.content).toEqual(stringToBytes("Test attachment"));
        done();
      }, done.fail);
    });