RFR: 7903932: Make private static classes final and have a private constructor

[Nizar Benalla]

On Fri, 17 Jan 2025 07:41:53 GMT, Nizar Benalla <nbenalla at openjdk.org> wrote:

> Please review this patch to make static utility classes final with a private constructor, as they are not meant to be extended.
> 
> This is a small refractor of the generated code.
> 
> TIA

I believe some of the panamization work included manually making these classes `final`, this was meant to prevent the need of manually modifying these files. I opened this PR to see if there is interest in doing this.

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PR Comment: https://git.openjdk.org/jextract/pull/274#issuecomment-2598221589