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.
if (!this.contentVisible) {
      return;
    }
    this.save();
    this.baseTransformStack.push(this.baseTransform);
    if (Array.isArray(matrix) && matrix.length === 6) {
      this.transform.apply(this, matrix);
    }
    this.baseTransform = this.ctx.mozCurrentTransform;
    if (bbox) {
      const width = bbox[2] - bbox[0];
      const height = bbox[3] - bbox[1];
      this.ctx.rect(bbox[0], bbox[1], width, height);
      this.current.updatePathMinMax(
        this.ctx.mozCurrentTransform,
        bbox[0],
        bbox[1]
      );
      this.current.updatePathMinMax(
        this.ctx.mozCurrentTransform,
        bbox[2],
        bbox[3]
      );
      this.clip();
      this.endPath();
    }
  }
  paintFormXObjectEnd() {