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.
}
    }
    ctx.putImageData(chunkImgData, 0, i * FULL_CHUNK_HEIGHT);
  }
}
function copyCtxState(sourceCtx, destCtx) {
  const properties = [
    "strokeStyle",
    "fillStyle",
    "fillRule",
    "globalAlpha",
    "lineWidth",
    "lineCap",
    "lineJoin",
    "miterLimit",
    "globalCompositeOperation",
    "font",
  ];
  for (let i = 0, ii = properties.length; i < ii; i++) {
    const property = properties[i];
    if (sourceCtx[property] !== undefined) {
      destCtx[property] = sourceCtx[property];
    }
  }
  if (sourceCtx.setLineDash !== undefined) {
    destCtx.setLineDash(sourceCtx.getLineDash());
    destCtx.lineDashOffset = sourceCtx.lineDashOffset;
  }
}
function resetCtxToDefault(ctx) {