RFR: 8350572: ZGC: Enhance z_verify_safepoints_are_blocked interactions with VMError

[Axel Boldt-Christmas]

If VMError reporting is triggered from a disallowed  thread state `z_verify_safepoints_are_blocked` will cause reentrant assertions to be triggered, when for example when loading the thread oop as part of thread printing. This extends the verification to be ignored if triggered from the thread doing the error reporting. In most cases performing the load barriers from disallowed thread states during error reporting will work.

Testing:
 - tier 1 Oracle supported platforms
 - GHA

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Commit messages:
 - 8350572: ZGC: Enhance z_verify_safepoints_are_blocked interactions with VMError

Changes: https://git.openjdk.org/jdk/pull/23820/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23820&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8350572
  Stats: 8 lines in 1 file changed: 8 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/23820.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23820/head:pull/23820

PR: https://git.openjdk.org/jdk/pull/23820