RFR: 8356255: Add Stable Field Updaters to allow efficient lazy field evaluations [v7]

[ExE Boss]

On Wed, 7 May 2025 15:03:57 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> This sketch shows how "Stable Updaters" can be used to create stable computations of `@Stable` fields. Only one updater is needed per class, similar to `AtomicIntegerFieldUpdater`.
>
> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Reformat

`StableFieldUpdater​.checkAndAdapt(…)` also performs an implicit null‑check:

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

PR Review: https://git.openjdk.org/jdk/pull/25040#pullrequestreview-2822161491