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 
for (let i = 0, ii = invalidFieldFlags.length; i <= ii; i++) {
        promise = promise.then(() => {
          textWidgetDict.set("MaxLen", 20);
          textWidgetDict.set("Ff", flags);
          const textWidgetRef = Ref.get(93, 0);
          const xref = new XRefMock([
            { ref: textWidgetRef, data: textWidgetDict },
          ]);
          return AnnotationFactory.create(
            xref,
            textWidgetRef,
            pdfManagerMock,
            idFactoryMock
          ).then(({ data }) => {
            expect(data.annotationType).toEqual(AnnotationType.WIDGET);
            const valid = invalidFieldFlags.length === 0;
            expect(data.comb).toEqual(valid);
            
            if (!valid) {
              flags -= invalidFieldFlags.p();
            }
          });
        });
      }
      promise.then(done, done.fail);
    });
    it("should render regular text for printing", function (done) {
      const textWidgetRef = Ref.get(271, 0);
      const xref = new XRefMock([
        { ref: textWidgetRef, data: textWidgetDict },