Support react-native platform-specific extension

From the react-native docs:

For example, say you have the following files in your project:

BigButton.ios.js
BigButton.android.js
You can then require the component as follows:

const BigButton = require('./BigButton');

This works since react-native ships a custom javascript bundler by default.

It would be good to have the possibility to generate such file names with bucklescript. Probably some sort of name mangling would be necessary.

Start by tracing how the compiler generates JavaScript filenames and review the linked React Native platform-specific extensions documentation. Determine how platform suffixes such as .ios.js and .android.js should be represented and generated, then verify that a component can be required without the suffix as in the example. No specific source file or test is named in the issue.