src/language-handlebars/postprocess.js/addBackslash
function addBackslash(/* options*/) {
  return {
    TextNode(node) {
      /* from the following template: `non-escaped mustache \\{{helper}}`
       * glimmer parser will produce an AST missing a backslash
       * so here we add it back
       * */
      if (node.chars.includes("\\")) {
        node.chars = node.chars.replace(/\\/, "\\\\");
      }
    },
  };
}