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.pendingClip) {
      this.current.updateClipFromPath();
    }
    if (!this.pendingClip) {
      this.compose(clipBox);
    }
    const ctx = this.ctx;
    if (this.pendingClip) {
      if (this.pendingClip === EO_CLIP) {
        ctx.clip("evenodd");
      } else {
        ctx.clip();
      }
      this.pendingClip = null;
    }
    this.current.startNewPathAndClipBox(this.current.clipBox);
    ctx.beginPath();
  }
  getSinglePixelWidth() {
    if (this._cachedGetSinglePixelWidth === null) {