Rename .babelrc.js to babel.config.js and enable caching

[shama]

Running the command:

npx ember-cli new hello-glimmerx --blueprint @glimmerx/blueprint

and then npm start in the project resulted in the error:

ERROR in ./src/index.js
Module build failed (from ./node_modules/babel-loader/lib/index.js):
Error: Caching was left unconfigured. Babel's plugins, presets, and .babelrc.js files can be configured
for various types of caching, using the first param of their handler functions:

module.exports = function(api) {
  // The API exposes the following:

  // Cache the returned value forever and don't call this function again.
  api.cache(true);

  // Don't cache at all. Not recommended because it will be very slow.
  api.cache(false);

  // Cached based on the value of some function. If this function returns a value different from
  // a previously-encountered value, the plugins will re-evaluate.
  var env = api.cache(() => process.env.NODE_ENV);

  // If testing for a specific env, we recommend specifics to avoid instantiating a plugin for
  // any possible NODE_ENV value that might come up during plugin execution.
  var isProd = api.cache(() => process.env.NODE_ENV === "production");

  // .cache(fn) will perform a linear search though instances to find the matching plugin based
  // based on previous instantiated plugins. If you want to recreate the plugin and discard the
  // previous instance whenever something changes, you may use:
  var isProd = api.cache.invalidate(() => process.env.NODE_ENV === "production");

  // Note, we also expose the following more-verbose versions of the above examples:
  api.cache.forever(); // api.cache(true)
  api.cache.never();   // api.cache(false)
  api.cache.using(fn); // api.cache(fn)

  // Return the value that will be cached.
  return { };
};

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This renames the blueprint .babelrc.js to babel.config.js and enables Babel's cache. The naming feels more consistent with the webpack.config.js naming and configuring the cache should avoid this error.