RFR: 8258254: Move PtrQueue flush to PtrQueueSet subclasses [v2]

[Kim Barrett]

> Please review this change to the PtrQueue hierarchy, changing queue flushing
> from an intrinsic operation of the queue to an operation the qset performs on
> a queue.  This is a piece of the refactoring being done under JDK-8258251,
> separated out for easier review.
> 
> This change also removes a couple of no longer used internal helper functions
> from PtrQueue.
> 
> Testing:
> mach5 tier1
> local (linux-x64) hotspot:tier1 with -XX:+UseShenandoahGC

Kim Barrett has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'master' into move_flush
 - update copyrights
 - move flush

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1851/files
  - new: https://git.openjdk.java.net/jdk/pull/1851/files/9b51552f..07d17089

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1851&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1851&range=00-01

  Stats: 38704 lines in 1385 files changed: 14517 ins; 11573 del; 12614 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1851.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1851/head:pull/1851

PR: https://git.openjdk.java.net/jdk/pull/1851