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 
partialEvaluator.xref = xref;
      AnnotationFactory.create(
        xref,
        textWidgetRef,
        pdfManagerMock,
        idFactoryMock
      )
        .then(annotation => {
          const id = annotation.data.id;
          const annotationStorage = {};
          annotationStorage[id] = { value: "こんにちは世界の" };
          return annotation._getAppearance(
            partialEvaluator,
            task,
            annotationStorage
          );
        }, done.fail)
        .then(appearance => {
          const utf16String =
            "\x30\x53\x30\x93\x30\x6b\x30\x61" +
            "\x30\x6f\x4e\x16\x75\x4c\x30\x6e";
          expect(appearance).toEqual(
            "/Tx BMC q BT /Goth 9 Tf 0 g 1 0 0 1 0 0 Tm" +
              ` 2.00 2.00 Td (${utf16String}) Tj ET Q EMC`
          );
          done();
        }, done.fail);
    });
    it("should not render a password for printing", function (done) {
      textWidgetDict.set("Ff", AnnotationFieldFlag.PASSWORD);