Undo moving of TurboModule to internal and expose utility function for TurboModule.class.isAssignableFrom (#43219)

Summary:
After discussing with mdvacca, we prefer to undo the change of `TurboModule` package to `.internal` as this is a quite aggressive breaking change for the ecosystem.

Moreover: users should not invoke `TurboModule.class.isAssignableFrom` because `TurboModule` is `.internal`. Therefore I'm exposing another API to check if a class is a TurboModule as a static field of `ReactModuleInfo`.

## Changelog:

[INTERNAL] - Do not use TurboModule.class.isAssignableFrom

Pull Request resolved: https://github.com/facebook/react-native/pull/43219

Test Plan: Tests are attached

Reviewed By: mdvacca, cipolleschi

Differential Revision: D54280882

Pulled By: cortinico

fbshipit-source-id: 9443c8aa23cf70dd5cfe574fe573d83313134358

packages/react-native-codegen/src/generators/modules/GenerateModuleJavaSpec.js

@@ -462,7 +462,7 @@ module.exports = {
         'com.facebook.react.bridge.ReactApplicationContext',
         'com.facebook.react.bridge.ReactContextBaseJavaModule',
         'com.facebook.react.bridge.ReactMethod',
-        'com.facebook.react.internal.turbomodule.core.interfaces.TurboModule',
+        'com.facebook.react.turbomodule.core.interfaces.TurboModule',
         'com.facebook.proguard.annotations.DoNotStrip',
         'javax.annotation.Nonnull',
       ]);