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

[dkrasnoff]

Great! Thanks for making one more project's build scripts more Kotlin 👍

[adam-enko]

Could you please rebase on a fresh master and resolve conflicts?

Done.

Please could you review this soon? It's difficult trying to keep migrated buildscripts up to date and resolving conflicts, especially because this PR has renamed the files.