RFR: 8302615: make JVMTI thread cpu time functions optional for virtual threads

[Serguei Spitsyn]

On Thu, 16 Feb 2023 18:05:54 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

> This is a minor JVM TI spec update for two timer functions `GetCurrentThreadCpuTime` and `GetThreadCpuTime` to allow implementations to support virtual threads.
> 
> The CSR is:
> [JDK-8302616](https://bugs.openjdk.org/browse/JDK-8302616): make JVMTI thread cpu time functions optional for virtual threads
> 
> No testing is needed.

Thank you for review, Alan.

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PR: https://git.openjdk.org/jdk/pull/12604