RFR: 8327990: [macosx-aarch64] JFR enters VM without WXWrite

[Richard Reingruber]

This pr changes  `JfrJvmtiAgent::retransform_classes()` and `jfr_set_enabled` to switch to `WXWrite` before transitioning to the vm.

Testing:
make test TEST=jdk/jfr/event/runtime/TestClassLoadEvent.java TEST_VM_OPTS=-XX:+AssertWXAtThreadSync
make test TEST=compiler/intrinsics/klass/CastNullCheckDroppingsTest.java TEST_VM_OPTS=-XX:+AssertWXAtThreadSync

More tests are pending.

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Commit messages:
 - Switch to WXWrite before entering the vm

Changes: https://git.openjdk.org/jdk/pull/18238/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18238&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327990
  Stats: 5 lines in 2 files changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/18238.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18238/head:pull/18238

PR: https://git.openjdk.org/jdk/pull/18238