Convert Gradle scripts from Groovy DSL to Kotlin DSL

[adam-enko]

The Kotlin DSL has many advantages over the Groovy DSL, making it easier to work with.

Some of kotlinx-benchmark's build scripts already use Kotlin DSL, and this PR converts the remaining ones.

I have intentionally tried to keep changes to a minimum, and focused on keeping the same behaviour. There should be no impact on the code or artifacts.

Part of https://youtrack.jetbrains.com/issue/KT-66764