RFR: 8354091: Update RELEASE_25 description for Flexible Constructor Bodies

[Iris Clark]

On Tue, 6 May 2025 00:10:08 GMT, Joe Darcy <darcy at openjdk.org> wrote:

> Getting ready for this SourceVersions change to be pushed after 
> 
>     JDK-8344703: Compiler Implementation for Flexible Constructor Bodies
>     
> is integrated.

Marked as reviewed by iris (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/25053#pullrequestreview-2816483412