Bug 1531

https://openjdk.org/jeps/472

Since JDK 17, the `java` command allowed passing '--enable-native-access=ALL-UNNAMED' (as well as '--add-open' etc).

Since JDK 24 the JVM is complaining about not having enabled such access
for certain java methods when called. See:

+++
WARNING: A restricted method in java.lang.System has been called
WARNING: java.lang.System::load has been called by com.jogamp.common.jvm.JNILibLoaderBase in an unnamed module (file:/usr/local/projects/JogAmp/gluegen/build-macosx/gluegen-rt.jar)
WARNING: Use --enable-native-access=ALL-UNNAMED to avoid a warning for callers in this module
WARNING: Restricted methods will be blocked in a future release unless native access is enabled
+++

Specify `jvmarg.modules` in GlueGen's make/jogamp-env.xml for all modules, 
also adding the '--add-open ...' directive for JOGL's' AWT access:

`--enable-native-access=ALL-UNNAMED --add-opens java.desktop/sun.awt=ALL-UNNAMED --add-opens java.desktop/sun.awt.windows=ALL-UNNAMED --add-opens java.desktop/sun.java2d=ALL-UNNAMED`

Also define jvmarg.generic = ${jvmarg.modules},
to be used for all `java` invocations of our unit tests.

Further supplement these arguments to our test scripts.