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.
m[1] * c + m[3] * d,
      m[0] * e + m[2] * f + m[4],
      m[1] * e + m[3] * f + m[5],
    ];
    ctx._originalTransform(a, b, c, d, e, f);
  };
  ctx.setTransform = function ctxSetTransform(a, b, c, d, e, f) {
    this._transformMatrix = [a, b, c, d, e, f];
    ctx._originalSetTransform(a, b, c, d, e, f);
  };
  ctx.resetTransform = function ctxResetTransform() {
    this._transformMatrix = [1, 0, 0, 1, 0, 0];
    ctx._originalResetTransform();
  };
  ctx.rotate = function ctxRotate(angle) {
    const cosValue = Math.cos(angle);
    const sinValue = Math.sin(angle);
    const m = this._transformMatrix;
    this._transformMatrix = [
      m[0] * cosValue + m[2] * sinValue,
      m[1] * cosValue + m[3] * sinValue,
      m[0] * -sinValue + m[2] * cosValue,
      m[1] * -sinValue + m[3] * cosValue,
      m[4],
      m[5],
    ];
    this._originalRotate(angle);
  };
}
class CachedCanvases {