RFR: 8355022: Implement JEP 506: Scoped Values [v7]

[Andrew Haley]

> Propose to finalize scoped values.
> The only functional change is that the orElse() method no longer accepts a null argument.

Andrew Haley has updated the pull request incrementally with one additional commit since the last revision:

  Fix merge

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Changes:
  - all: https://git.openjdk.org/jdk/pull/24923/files
  - new: https://git.openjdk.org/jdk/pull/24923/files/8354bcb5..7d354394

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24923&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24923&range=05-06

  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/24923.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24923/head:pull/24923

PR: https://git.openjdk.org/jdk/pull/24923