Improve file type check for AAR

[Copilot]

Replaces the extension-only check for AAR files with a content-based inspection, fixing both false negatives (real AARs with .jar extension slipping through) and false positives (non-AAR files with .aar extension incorrectly blocked).

Changes

• ShadowJar.kt: Replace file.extension.equals("aar", ignoreCase = true) with file.isAar() — a private extension that opens the file as a ZipFile and checks for the presence of AndroidManifest.xml (mandatory in the AAR spec). Catches ZipException only, so real I/O errors still propagate.
• JavaPluginsTest.kt: Update failBuildIfProcessingAar to use a real AAR-shaped ZIP (via buildJar + AndroidManifest.xml entry) instead of an empty file. Add failBuildIfProcessingAarWithJarExtension to cover the previously undetected case where an AAR is named with a .jar extension.

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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:

• dl.google.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)
  • Triggering command: /usr/bin/curl curl -s REDACTED -o /tmp/test-download.jar (dns block)
• 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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