RFR: 8152844: JVM InstanceKlass Methods For Obtaining Package/Module Should Be Moved to Klass

[Rachel Protacio]

Hello,

Please review this fix for the package() and module() functions, making 
them pure virtual functions of Klass and implementing them in the 
relevant child classes. This cleans up some verbose and repetitive code 
that was casting and checking klass types. Also added test cases to 
runtime/modules/getModuleJNI/GetModule.java, ensuring that all the 
module() functions work as expected.

Bug: https://bugs.openjdk.java.net/browse/JDK-8152844
Open webrev: http://cr.openjdk.java.net/~rprotacio/8152844.00/

Tested with jtreg tests in jdk/test (java/lang, java/io, java/security, 
java/util, tools/jimage, tools/jlink, and tools/jmod), JPRT, and RBT 
hotspot and non-colo tests.

Thanks!
Rachel