RFR: JDK-8302666: Replace CHM with VarHandle in ForeachOrderedTask [v5]

[Viktor Klang]

> I noticed when looking at the code that there was no real need to use a CHM to perform the tracking of activation in an ordered fashion on ForEachOrderedTask, but instead a VarHandle can be used, reducing allocations and indirection.

Viktor Klang has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  Updating copyright header of ForEachOps.java and removing unnecessary suppression of an unchecked cast.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12320/files
  - new: https://git.openjdk.org/jdk/pull/12320/files/b4b241e2..a5c6b0d0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12320&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12320&range=03-04

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/12320.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12320/head:pull/12320

PR: https://git.openjdk.org/jdk/pull/12320