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);
    }
  } else if (imgData.kind === ImageKind.RGBA_32BPP) {
    
    const hasTransferMaps = !!(
      transferMapRed ||
      transferMapGreen ||
      transferMapBlue
    );
    j = 0;
    elemsInThisChunk = width * FULL_CHUNK_HEIGHT * 4;
    for (i = 0; i < fullChunks; i++) {
      dest.set(src.subarray(srcPos, srcPos + elemsInThisChunk));
      srcPos += elemsInThisChunk;
      if (hasTransferMaps) {
        for (let k = 0; k < elemsInThisChunk; k += 4) {
          if (transferMapRed) {
            dest[k + 0] = transferMapRed[dest[k + 0]];
          }
          if (transferMapGreen) {
            dest[k + 1] = transferMapGreen[dest[k + 1]];
          }
          if (transferMapBlue) {
            dest[k + 2] = transferMapBlue[dest[k + 2]];
          }
        }
      }
      ctx.putImageData(chunkImgData, 0, j);
      j += FULL_CHUNK_HEIGHT;