function generateFormattedCodeFromAST(babelNode) {
  return generate(babelNode, {comments: true}, '').code.trim();
}
Generate formatted JS source code from a given Babel AST object.
Note: JS comments are preserved.
See `__tests__/TestUtil-test.js` for example.

@param {BabelNode} babelNode BabelNode object obtained after parsing JS code
or from a Babel Transform.
@return {string} JS source code