RFR: 8314019: Add gc logging to jdk/jfr/event/gc/detailed/TestZAllocationStallEvent.java

[Stefan Karlsson]

Add GC logging to this test so that we can figure out why this is intermittently throwing OOME.

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Commit messages:
 - 8314019: Add gc logging to jdk/jfr/event/gc/detailed/TestZAllocationStallEvent.java

Changes: https://git.openjdk.org/jdk/pull/15207/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15207&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314019
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/15207.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15207/head:pull/15207

PR: https://git.openjdk.org/jdk/pull/15207