RFR: 8323159: Consider adding some text re. memory zeroing in Arena::allocate [v3]

[Maurizio Cimadamore]

On Fri, 12 Jan 2024 13:06:39 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> This PR proposes to add a clarification that an `Arena` always returns zeroed-out segments for `Arena::allocate` methods.
>> 
>> Note that other overloaded methods refer to the abstract `Arena::allocate` method via implementation notes.
>
> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Move documentation of zero init to each Arena factory

Marked as reviewed by mcimadamore (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/17308#pullrequestreview-1818210976