RFR: 8354996: Reduce dynamic code generation for a single downcall [v3]

[Chen Liang]

On Sun, 4 May 2025 21:43:40 GMT, Chen Liang <liach at openjdk.org> wrote:

>> Hmm, I intentionally checked `toSet` does not reject duplicates but forgot about this part. Anyways this stream code is problematic; will fix this in a patch that removes this stream code wholesale.
>
> I created an issue to revisit CapturableState https://bugs.openjdk.org/browse/JDK-8356126 and will fix these problem with new unit test ensuring the toString message and nonexistent/duplicate behaviors, also removing redundant stream usage.

See #25025, which includes a regression test that should prevent such duplicate arg mishandling or toString message missing user-friendly names.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24742#discussion_r2072730363