Introduce method for performing a batch of operations against a context

[eliperelman]

Allows passing a function to execute against a certain context. Basically the non-conditional version of .when().

config
  .resolve
    .batch((resolve) => {
      resolve.modules.add(MODULES);
      resolve.extensions.add('.jsx');
      resolve.alias.set('react-native', 'react-native-web');
    });

config
  .resolve
    .batch(({ modules, extensions, alias }) => {
      modules.add(MODULES);
      extensions.add('.jsx');
      alias.set('react-native', 'react-native-web');
    });

Helps avoid things like:

config
  .resolve
    .modules
      .add(MODULES)
      .end()
    .extensions
      .add('.jsx')
      .end()
    .alias
      .set('react-native', 'react-native-web');