This is a regression from #12864. The underscore is now too thin when the document is zoomed in.

URL: https://github.com/mozilla/pdf.js/files/2321540/issue6127.pdf
PDF.js 2.7.526: https://i.imgur.com/T4mIpct.png
PDF.js 2.7.510: https://i.imgur.com/nbwEpGT.png
Adobe Acrobat Reader DC 2020.013.20074: https://i.imgur.com/wDFBf3R.png

The screenshots were taken at 400% zoom.
this.suspendedCtx = suspendedCtx;
    }
    if (group.smask) {
      this.tempSMask = this.smaskStack.pop();
      this.restore();
    } else {
      this.ctx.restore();
      const currentMtx = this.ctx.mozCurrentTransform;
      this.restore();
      this.ctx.save();
      this.ctx.setTransform.apply(this.ctx, currentMtx);
      const dirtyBox = Util.getAxialAlignedBoundingBox(
        [0, 0, groupCtx.canvas.width, groupCtx.canvas.height],
        currentMtx
      );
      this.ctx.drawImage(groupCtx.canvas, 0, 0);
      this.ctx.restore();
      this.compose(dirtyBox);
    }
  }
  beginAnnotations() {
    this.save();
    if (this.baseTransform) {
      this.ctx.setTransform.apply(this.ctx, this.baseTransform);
    }
  }
  endAnnotations() {
    this.restore();
  }
  beginAnnotation(id, rect, transform, matrix, hasOwnCanvas) {