Fix EAP compatibility and component model completion

[bbeny123]

Building and running tests against the latest IntelliJ IDEA EAP requires newer platform integration and JDK 25.

This MR:

• upgrades the IntelliJ Platform Gradle Plugin to 2.19.0,
• switches EAP CI to JDK 25,
• makes the Java toolchain follow the JVM running Gradle while retaining Java 21 bytecode compatibility.

With 2.19.0, tests load all bundled IDE plugins, exposing unrelated file path suggestions inside componentModel values. Restricting the test environment to selected plugins would hide this completion issue, so this MR fixes the contributor itself. It now runs first and stops subsequent contributors in that context, leaving only MapStruct’s component model suggestions.

The completion test is also updated to verify automatic insertion when only one component model matches.

[hduelme]

Thanks a lot, @bbeny123! We haven’t had time to look into the EAP issue ourselves in a while.