RFR: 8373335: Serial: Clean up SerialHeap members by access specifies [v2]

[Albert Mingkun Yang]

On Tue, 9 Dec 2025 10:28:05 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Trivial moving member of `SerialHeap` so that all `private` fields/methods are altogether (at the top).
>>  
>> Test: tier1
>
> Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review

Thanks for review.

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PR Comment: https://git.openjdk.org/jdk/pull/28718#issuecomment-3637013763