src/language-html/print-preprocess.js/removeIgnorableFirstLf
function removeIgnorableFirstLf(ast /*, options */) {
  return ast.map((node) => {
    if (
      node.type === "element" &&
      node.tagDefinition.ignoreFirstLf &&
      node.children.length !== 0 &&
      node.children[0].type === "text" &&
      node.children[0].value[0] === "\n"
    ) {
      const [text, ...rest] = node.children;
      return node.clone({
        children:
          text.value.length === 1
            ? rest
            : [text.clone({ value: text.value.slice(1) }), ...rest],
      });
    }
    return node;
  });
}