Improve VirtualThread instrumentation

[PerfectSlayer]

What Does This Do

This PR addresses the following issue with VirtualThread instrumentation:

• Stop instrumenting VirtualThread as a Runnable when virtual thread instrumentation is enabled
• A regression introduced in Fix VirtualThread support on multiple unmount/remount cycles  #10931 / Fix virtual thread propagation on thread remounts #10887 that instruments both afterDone() and afterDone(boolean) leading to duplicate clearing work

Motivation

I did not check at bytecode level the changes from the original PRs and that was wrong.

Additional Notes

Contributor Checklist

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Jira ticket: [PROJ-IDENT]

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