8077203: Avoid unnecessary stripping of package names from FQN's in is_same_class_package() methods

[harold seigel]

Hi,

Please review this JDK-10 fix for JDK-8077203.  The fix improves the 
JVM's is_same_class_package() methods by removing one of them and by 
changing the implementation of  'is_same_class_package(oop, const 
Symbol*)' to get the package name for 'this'  from its package entry 
record, instead of parsing its class name.

Open Webrev: 
http://cr.openjdk.java.net/~hseigel/bug_8077203/webrev/index.html

JBS Bug: https://bugs.openjdk.java.net/browse/JDK-8077203

The fix was tested with JCK Lang and VM tests, the JTreg hotspot, 
java/io, java/lang, java/util and other tests, the co-located NSK tests, 
and with JPRT.

Thanks, Harold