RFR (L) JDK-8230199: consolidate signature parsing code in HotSpot sources

[Lois Foltan]

Please review the following enhancement to consolidate signature parsing 
code in Hotspot sources.  This change removes duplicate blocks of code 
that parse field or method signatures, provides a new Signature class to 
support basic signature queries on Symbol operands and enhances the 
SignatureStream class to parse field signatures in addition to methods.

open webrev 
at:http://cr.openjdk.java.net/~lfoltan/bug_jdk8230199.0/webrev/ 
<http://cr.openjdk.java.net/~lfoltan/bug_jdk8230199.0/webrev/>
bug link: https://bugs.openjdk.java.net/browse/JDK-8230199
contributed-by: Lois Foltan, John Rose

Testing: hs-tier1-8, jdk-tier1-2

Thanks,
Lois