RFR: 8287281: adjust guarantee in Handshake::execute for the case of target thread being current [v6]

[Serguei Spitsyn]

On Mon, 13 Jun 2022 11:42:43 GMT, David Holmes <dholmes at openjdk.org> wrote:

> Maybe we actually need to backtrack and restore an invariant that there is always a TLH even for the current thread and fix the JVMTI code that did things differently?

This will make JVMTI code unnecessarily ugly in a couple of spots.
But I'm okay with that if keeping this invariant is important.
I can help with fixing JVMTI if needed.

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PR: https://git.openjdk.org/jdk/pull/8992