Properly handle null values coming from JS (#49250)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/49250

The TurboModule System decided to ignore the Null values when they are coming to JS. However, in iOS, null value can be mapped to `[NSNull null];` and this value is a valid value that can be used on the native side.

In the old architecture, when the user were sending a null value from JS to a native module, the Native side was receiving the value.

In the New Architecture, the value was stripped away.

This change allow us to handle the `null` value properly in the interop layer, to restore the usage of legacy modules in the New Arch.

I also tried with a more radical approach, but several tests were crashing because some modules do not know how to handle `NSNull`.

See discussion happening here: https://github.com/invertase/react-native-firebase/issues/8144#issuecomment-2548067344

## Changelog:
[iOS][Changed] - Properly handle `null` values coming from NativeModules.

Reviewed By: sammy-SC

Differential Revision: D69301396

fbshipit-source-id: be275185e2643092f6c3dc2481fe9381bbcf69e9