[b-pm]

Fixes #1276

Summary

Adds a testTargetJavaVersion build-parameters property (default 17) so test bytecode --release is configurable the same way targetJavaVersion is for main sources.

• build-logic/build-parameters: new testTargetJavaVersion (default 17, mandatory)
• build-logic.java.gradle.kts: compileTestJava uses buildParameters.testTargetJavaVersion instead of a hardcoded 17
• ToolchainProperties.kt: Gradle check that testTargetJavaVersion >= 17 and that the resolved test JDK is at least that value
• DEVELOPMENT.md: example -PtestTargetJavaVersion=21

Verify

./gradlew parameters   # lists testTargetJavaVersion
./gradlew compileTestJava
./gradlew compileTestJava -PtestTargetJavaVersion=21
# expected failure (below floor):
./gradlew help -PtestTargetJavaVersion=11

AI disclosure

This PR was prepared with AI assistance (coding agent). I reviewed the change and can explain it. I will answer any maintainer questions myself.

DCO

I will add my Signed-off-by via git commit --amend -s / git commit -s after opening; this commit intentionally has no agent-added DCO trailer per Sigstore AI_POLICY.md.

[loosebazooka]

I would need some reasoning behind why this is required. What does this unlock for you?

[b-pm]

I picked it partially because it was an open issue and I realized that this would be very helpful in supporting newer JDKs.