RFR: 8341903: Implementation of Scoped Values (Fourth Preview) [v7]

[Andrew Haley]

> The fourth preview of scoped values.

Andrew Haley 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 10 additional commits since the last revision:

 - Merge https://github.com/openjdk/jdk into JDK-8341903
 - Typo in comment. (Thanks, Roland!)
 - API change
 - Merge branch 'clean' into JDK-8341903
 - Scoped values
 - Scoped values
 - Fix javadoc
 - Scoped Values API changes
 - Scoped Values API changes
 - Scoped Values API changes

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21456/files
  - new: https://git.openjdk.org/jdk/pull/21456/files/bc3bdc10..84a436cc

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21456&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21456&range=05-06

  Stats: 115145 lines in 2059 files changed: 43921 ins; 63558 del; 7666 mod
  Patch: https://git.openjdk.org/jdk/pull/21456.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21456/head:pull/21456

PR: https://git.openjdk.org/jdk/pull/21456