Unit Tests - Android + Kotlin

[mvarendorff]

What does this PR do?

This PR adds generated unit tests to Android and Kotlin SDKs. It also contains some refactoring to generate similar classes from the same template to both the Android and Kotlin SDK, similar to how Dart and Flutter share templates.

Test Plan

I set up the generated project locally and ran the respective test command (./gradlew library:test for the Android SDK (requires Java 8-11 not higher!) and ./gradlew test for the Kotlin SDK)

Related PRs and Issues

• #680

Have you read the Contributing Guidelines on issues?

Yup

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Discord username for swag as requested by Tessa: yestheory