RFR: 8227054: ServiceThread needs to know about all OopStorage objects

[Kim Barrett]

8227054: ServiceThread needs to know about all OopStorage objects
8227053: ServiceThread cleanup of OopStorage is missing some

Please review this change in how OopStorage objects are managed and
accessed.  There is a new (all static) class, OopStorages, which
provides infrastructure for creating all the storage objects, access
via an enum-based id, and iterating over them.

Various components that previously managed their own storage objects 
now obtain them from OopStorages.  A number of access functions have
been eliminated as part of that, though some have been retained for
internal convenience of a component.

The set of OopStorage objects is now declared in one place, using
x-macros, with collective definitions and usages ultimately driven off
those macros.  This includes the ServiceThread (which no longer needs
explicit knowledge of the set, and is no longer missing any) and the
OopStorage portion of WeakProcessorPhases.  For now, the various GCs
still have explicit knowledge of the set; that will be addressed in
followup changes specific to each collector.  (This delay minimizes
the impact on Leo's in-progress review that changes ParallelGC to use
WorkGangs.)

This change also includes a couple of utility macros for working with
x-macros.

CR:
https://bugs.openjdk.java.net/browse/JDK-8227054
https://bugs.openjdk.java.net/browse/JDK-8227053

Webrev:
http://cr.openjdk.java.net/~kbarrett/8227054/open.00/

Testing:
mach5 tier1-3