RFR(S) 8241071 Generation of classes.jsa is not deterministic

[Ioi Lam]

https://bugs.openjdk.java.net/browse/JDK-8241071
http://cr.openjdk.java.net/~iklam/jdk15/8241071-deterministic-cds-archive.v02/

The goal is to for "java -Xshare:dump" to produce deterministic contents in
the CDS archive that depend only on the contents of $JAVA_HOME/lib/modules.

Problems:
[1] Symbols in the CDS archive may have non-deterministic order because
     Arena allocation is non-deterministic.
[2] The contents of the CDS shared heap region may be randomized due to
     ImmutableCollections.SALT32L.

Fixes:
[1] With -Xshare:dump, allocate Symbols from the class space (64-bit only).
     See changes in symbol.cpp for details.
[2] When running the VM with -Xshare:dump, ImmutableCollections.SALT32L is
     initialized with a deterministic seed. NOTE: this affects ONLY when the
     VM is running with the special flag -Xshare:dump to dump the CDS 
archive.
     It does NOT affect normal execution of Java programs.

---
I also cleaned up the -Xlog:cds output and print out the CRC of each
CDS region, to help diagnose why two CDS archives may have different 
contents.

Thanks
- Ioi