RFR: 8367859: Remove nio exception gensrc

[Brian Burkhalter]

On Wed, 17 Sep 2025 18:57:45 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

> An alternative implementation to https://github.com/openjdk/jdk/pull/27338, which removes the entire gensrc stage and instead permanently checks in the generated Java files.

Looks all right.

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Marked as reviewed by bpb (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/27352#pullrequestreview-3241093519