Fixed two build issues preventing Android plugin compilation:
1. Build script now builds from test app context instead of standalone
- Capacitor Android is only available as a project dependency, not from Maven
- Plugin must be built within a Capacitor app's Android project
- Changed build_plugin_for_test_app() to build from test app's android/
directory where Capacitor is available as :capacitor-android project
2. Added JVM arguments for Java 17+ KAPT compatibility
- Java 21's module system blocks KAPT from accessing internal compiler classes
- Added --add-opens flags to both org.gradle.jvmargs and kotlin.daemon.jvmargs
- Kotlin compiler daemon runs separately and needs its own configuration
- Applied to both plugin and test app gradle.properties files
These changes allow the plugin to build successfully with Java 21 and ensure
it's built in the correct context where Capacitor dependencies are available.
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