RFR: 8296323: JVMTI can_support_virtual_threads not available for agents loaded into running VM [v5]

[Serguei Spitsyn]

On Mon, 21 Nov 2022 20:19:47 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

>> The can_support_virtual_thread was initially implemented as an onload capability.
>> It is why this capability does not work for the agents loaded into running VM.
>> The fix is to move it from `onload` to `always`capabilities list.
>> 
>> Testing:
>> New test is added: VirtualStartThreadTest.
>> TBD: mach5 jvmti, jdi and tier1-6 tests.
>
> Serguei Spitsyn has updated the pull request incrementally with one additional commit since the last revision:
> 
>   minor update for unnamed threads in jvmti_common.h

Alan and Richard, thank you for reviews.

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PR: https://git.openjdk.org/jdk/pull/11246