RFR: 8254883: ZGC: Make the ZArrayIterator reusable for ZRelocationSetIterators [v2]

[Per Liden]

> The ZRelocationSetIterators are mostly just duplicate implementations of the ZArrayIterators. With some slight
> adjustments to ZArrayIteratorImpl we can make that code reusable for ZRelocationSetIteratorImpl.
> Note that this PR builds/depends on "8254878: Move last piece of ZArray to GrowableArray", which is out for review as a
> separate PR (https://github.com/openjdk/jdk/pull/694).

Per Liden has updated the pull request incrementally with one additional commit since the last revision:

  Make iterator members const pointers

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/697/files
  - new: https://git.openjdk.java.net/jdk/pull/697/files/7c09a198..dd59735a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=697&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=697&range=00-01

  Stats: 9 lines in 2 files changed: 0 ins; 0 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk/pull/697.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/697/head:pull/697

PR: https://git.openjdk.java.net/jdk/pull/697