Extend visibility of Custom Moshi Adapters

[cortinico]

I'm extending the visibility of the custom Moshi Adapters TypesAdapterFactory and XNullableAdapterFactory from internal to public. This will support the use case of developers that want to initialise their own Moshi instance and want to provide custom Type adapters on top of the generated ones.

Fore more context see the doc here

    /**
     * Creates everything needed for retrofit to make it work with the client lib, including a
     * [Moshi] instance. If you want to use your own instance of moshi, use
     * converterFactory(moshi) instead, and add [XNullableAdapterFactory], [KotlinJsonAdapterFactory] and
     * [TypesAdapterFactory] to your moshi builder (in a similar way how we are instantiating the `moshi` field here).
     */