Fix missing junit-platform-launcher version

[DidierLoiseau]

What's changed?

Use the JUnit BOM to specify the version of all JUnit dependencies.

Since rewrite-test uses JUnit as an api() dependency, this is done through api(platform(…)) instead of testImplementation(platform(…)).

What's your motivation?

I tried to build OpenRewrite on my Linux Desktop machine, and I kept getting the following error:

> Task :rewrite-java-17:compatibilityTest FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':rewrite-java-17:compatibilityTest'.
> Could not resolve all files for configuration ':rewrite-java-17:compatibilityTestRuntimeClasspath'.
   > Could not find org.junit.platform:junit-platform-launcher:.
     Required by:
         project :rewrite-java-17

(also with the other rewrite-java-* modules)

I don’t really understand why it works in other environments, but the thing is that the junit-platform-launcher version wasn’t specified anywhere.

JUnit documentation suggests using their BOM to align dependency versions. I thought it couldn’t hurt anyway, and this allows centralizing the version of JUnit (though I kept latest.release for now)

Anything in particular you'd like reviewers to focus on?

I am not very familiar with Gradle so better double check this 🙂

Have you considered any alternatives or workarounds?

This is the only solution I found but maybe I should have posted a question as well 😏

Checklist

• I've added unit tests to cover both positive and negative cases – N/A
• I've read and applied the recipe conventions and best practices – N/A
• I've used the IntelliJ IDEA auto-formatter on affected files – actually I get different formatting if I do that on rewrite-java-8/build.gradle.kts