Fix Log4j2PluginsCacheFileTransformer not working for merging Log4j2Plugins.dat files

[Copilot]

Ports the Log4j2PluginsCacheFileTransformer fixes from #1175 to the Groovy plugin branch.

Transformer fixes (Log4j2PluginsCacheFileTransformer.groovy)

• canTransformResource: Use element.relativePath.pathString instead of element.name — prevents false matches on .dat files with the same name in unrelated paths
• hasTransformedResource: Simplify to !temporaryFiles.isEmpty() — old logic incorrectly returned false for single-file transforms without relocators
• modifyOutputStream: Wrap in try/finally so temp files are always cleaned up
• deleteTempFiles(): New helper that removes files from both the list and filesystem (vs. just clear())
• relocatePlugins: Made package-accessible for testing
• Updated Javadoc to reference upstream Apache source

Test updates (Log4j2PluginsCacheFileTransformerSpec.groovy)

• Extend TransformerSpecSupport to get getFileElement() helper
• Add canTransformResource test asserting full-path matching semantics
• Replace should not transformer / should transform with transformAndModifyOutputStream covering the full pipeline
• Add relocations parameterized test (matching and non-matching pattern cases)

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• CHANGELOG's "Unreleased" section has been updated, if applicable.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• scans-in.gradle.com
  • Triggering command: /usr/lib/jvm/temurin-17-jdk-amd64/bin/java /usr/lib/jvm/temurin-17-jdk-amd64/bin/java --add-opens=java.base/java.lang=ALL-UNNAMED --add-opens=java.base/java.lang.invoke=ALL-UNNAMED --add-opens=java.base/java.util=ALL-UNNAMED --add-opens=java.prefs/java.util.prefs=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED --add-opens=java.base/java.util=ALL-UNNAMED --add-opens=java.prefs/java.util.prefs=ALL-UNNAMED --add-opens=java.base/java.nio.charset=ALL-UNNAMED --add-opens=java.base/java.net=ALL-UNNAMED --add-opens=java.base/java.util.concurrent=ALL-UNNAMED --add-opens=java.base/java.util.concurrent.atomic=ALL-UNNAMED --add-opens=java.xml/javax.xml.namespace=ALL-UNNAMED --add-opens=java.base/java.time=ALL-UNNAMED -Xmx4g -Dfile.encoding=UTF-8 -Duser.country -Duser.language=en -Duser.variant (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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