RFR: 8296492: Remove ObjectLocker in JVMTI get_subgroups call [v2]

[Coleen Phillimore]

On Tue, 8 Nov 2022 12:47:29 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Handle non OOM exceptions and rename subgroupsAsArray.
>
> I wonder if the intermediate resource array is needed now. With the change, subgroupsAsArray returns a Java array,  JvmtiEnvBase::get_subgroups creates a resource array with a handle to each of the thread group oops, then JvmtiEnvBase::new_jthreadArray creates a new local ref for each group.

@AlanBateman you're right the extra copy of the thread group array is wasteful and since I've changed this code already, I cleaned up the extra copying.  Reran jvmti tests.

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PR: https://git.openjdk.org/jdk/pull/11033