Kotlin: fix static code analysis weak warnings (3/n) (#52206)

Summary:
Static code analysis reports several weak warnings, many of which seem to be leftovers after Kotlin migration. This PR addresses quite a few:

- [Return or assignment can be lifted out](https://www.jetbrains.com/help/inspectopedia/LiftReturnOrAssignment.html)
- [Verbose nullability and emptiness check](https://www.jetbrains.com/help/inspectopedia/VerboseNullabilityAndEmptiness.html)
- [Size check can be replaced with 'isNotEmpty()'](https://www.jetbrains.com/help/inspectopedia/ReplaceSizeCheckWithIsNotEmpty.html)

## Changelog:

[INTERNAL] - Kotlin: fix static code analysis weak warnings (3/n)

Pull Request resolved: https://github.com/facebook/react-native/pull/52206

Test Plan:
```sh
yarn android
yarn test-android
```

Reviewed By: javache

Differential Revision: D77209766

Pulled By: cortinico

fbshipit-source-id: c154ec6578125c16ad37c9dd15295a2edcacee4a