Updated to `source-map-explorer` and uses the standard Metro bundler

This version switches to using the awesome source-map-explorer package which can visualize the output from the Metro bundler directly. This means that the Haul bundler is no longer used and it should therefore result in less build errors and more accurate results. The source-map-explorer package also provides an interactive User interface which allows you to navigate deeper into the source code.
Additionally, you can now run this version directly using npx without having to install any dependencies.

To use, just run npx react-native-bundle-visualizer@next