RFR: 8342560: GenShen: Fix confusing method name [v2]

[William Kemper]

On Fri, 18 Oct 2024 16:26:44 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> Rename `is_old` to make it more clear that this about pointers that are outside the scope of a young collection.
>
> William Kemper has updated the pull request incrementally with six additional commits since the last revision:
> 
>  - Use an even better name, add an explanatory comment
>  - 8342564: GenShen: Only reference young/old generation names in generational mode
>    
>    Reviewed-by: xpeng, ysr
>  - 8342214: GenShen: Reduce code duplication in shFreeSet with iterator abstraction
>    
>    Reviewed-by: kdnilsen, ysr
>  - 8342239: GenShen: Revert changes in adaptive heuristic to avoid overflow on 32 bit
>    
>    Reviewed-by: ysr
>  - 8342278: GenShen: Move non-generational mode test out of generational test configuration
>    
>    Reviewed-by: ysr
>  - 8342255: GenShen: Remove unnecessary enum initial values
>    
>    Reviewed-by: ysr

This PR is pulling commits from a rebased merge now. I might have to clean this up and force a push.

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PR Comment: https://git.openjdk.org/shenandoah/pull/517#issuecomment-2422873214