dillon1000/react

Pass environment options through babel plugin

Updates the babel plugin so that environment options — including custom hook 
definitions — can be passed in through the plugin: 

* Renames `CompilerFlags` => `PluginOptions` since they are specific to the 
babel plugin, and are no longer just flags. 

* Moves the definition of `useFreeze()` out of the builtin hook list and instead 
passes it when our unit tests configure the plugin.