RN project wide Kotlin version (#31645)

Summary:
This PR sets project wide Kotlin version to 1.4.21, supported in Buck https://github.com/facebook/buck/tree/dev/third-party/java/kotlin.

We had to specify version for both kotlin-dsl and kotlin('jvm') plugins to remove version mismatch warnings in **react-native-gradle-plugin**. Also I expect more Kotlin code in RN, so instead of specifying version for each sub-project it's better to have project wide setting.

We don't need to load Kotlin in react-native-gradle-plugin because Kotlin is available RN project wide.

## Changelog

[Internal] [Changed] - Project wide Kotlin version set to 1.4.21

Pull Request resolved: https://github.com/facebook/react-native/pull/31645

Test Plan: Everything works as expected, no visible change for developers.

Reviewed By: yungsters

Differential Revision: D28991440

Pulled By: ShikaSD

fbshipit-source-id: 971fa6f50c12d916a56d0dcde7c65299496fb68a