RFR: 8351565: Implement JEP 502: Stable Values (Preview) [v33]

[Maurizio Cimadamore]

On Thu, 3 Apr 2025 08:22:47 GMT, Per Minborg <pminborg at openjdk.org> wrote:

> "A stable value is a holder of content that can be lazily computed at most once"

I'd replace `computed` with `set` (as that's the term we use in the API).

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PR Review Comment: https://git.openjdk.org/jdk/pull/23972#discussion_r2026860656