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

[Chen Liang]

On Thu, 8 May 2025 17:33:09 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> 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

Reviewed the Javadoc and specification updates and `@enablePreview` removals for the end of preview. These are all related tests that can have the directive removed, aside from the thread flock test I asked about.

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Marked as reviewed by liach (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/24923#pullrequestreview-2825991095