Attach per-version properties to parameterized Gradle versions

[ogolberg]

Summary

• Adds a @GradleVersion(version, properties = [@Property(key, value)]) sub-annotation so each Gradle version in a parameterized test can carry extra metadata (e.g. a matching Kotlin version to pair with an older Gradle).
• Both @TestKit and @ParameterizedWithGradleVersions gain a versions: Array<GradleVersion> field alongside the existing Array<String> form. Resolution priority: method versions → method value → class versions → class gradleVersions. Fully backward compatible.
• GradleVersionArgument carries the properties; ProjectKey includes them so the per-version TestProject cache stays correct.
• TestProject.property(key) exposes the metadata to test bodies.
• Display names include the properties, e.g. project(gradle: 8.6 [kotlin=1.9.24]).

Example

@TestKit(versions = [
    GradleVersion(version = "8.6", properties = [Property(key = "kotlin", value = "1.9.24")]),
    GradleVersion(version = "8.7", properties = [Property(key = "kotlin", value = "2.0.0")])
])
class MyTest {
    @ParameterizedWithGradleVersions
    fun test(project: TestProject) {
        val kotlin = project.property("kotlin")
        // use `kotlin` to template the build file, pick a plugin version, etc.
    }
}

Test plan

• New GradleVersionPropertiesIntegrationTest exercises the feature and passes
• Existing TestKitIntegrationTest still uses the legacy gradleVersions = [...] form unchanged
• Confirm display names render properties: project(gradle: 8.6 [kotlin=1.9.24])
• CI green across the :junit5 module

🤖 Generated with Claude Code