RFR (XS) JDK-8222502: Replace 19,20 case alternatives with JVM_CONSTANT_Module/Package names

[Lois Foltan]

Please review the following change to add JVM_CONSTANT_Module and 
JVM_CONSTANT_Package to classfile_constants.h and use these constant 
types instead of hard coded 19 & 20 within ClassFileParser.

open webrev at: http://cr.openjdk.java.net/~lfoltan/bug_jdk8222502.0/webrev/
bug link: https://bugs.openjdk.java.net/browse/JDK-8222502 
<https://bugs.openjdk.java.net/browse/JDK-8222502>

Testing: hs-tier1-3, jdk-tier1-3

Thanks,
Lois