RFR: 8292657: Calling GetLocalXXX from virtual thread with thread parameter set to NULL returns carrier locals

[Serguei Spitsyn]

If JVM TI GetLocalXXX/SetLocalXXX is called from a virtual thread with the thread parameter set to NULL (meaning current thread) then it should get/set the value of the locals in the virtual thread frames. Instead, it reads the carrier thread locals and/or crashes.

The fix is that the relevant checking of the jthread parameter for NULL and adjusting it to current thread is added.
It is done in new utility `function current_thread_obj_or_resolve_external_guard(jthread thread)`. For more convenient testing the same adjustment is done in the JVM TI extension function `GetCarrierThread()`.

The test serviceability/jvmti/vthread/GetSetLocalTest is updated to add previously missed test coverage.

The test serviceability/jvmti/vthread/VThreadTest has been updated to adopt to update behavior of the `GetCarrierThread`.

The fix was verified with the test/hotspot/jtreg/serviceability/jvmti/vthread/ tests.

The fix was also tested with the existing JVM TI and JDI tests to make sure no regressions are introduced.

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Commit messages:
 - 8292657: Calling GetLocalXXX from virtual thread with thread parameter set to NULL returns carrier locals

Changes: https://git.openjdk.org/jdk/pull/10051/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10051&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292657
  Stats: 41 lines in 6 files changed: 26 ins; 2 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/10051.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10051/head:pull/10051

PR: https://git.openjdk.org/jdk/pull/10051