RFR: 8346688: GenShen: Missing metadata trigger log message

[William Kemper]

The generational mode may trigger a global collection when metaspace is exhausted. When this happens, it should log this trigger as the reason for starting a cycle.

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Commit messages:
 - Missing metadata trigger log message in generational mode

Changes: https://git.openjdk.org/jdk/pull/22838/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22838&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346688
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/22838.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22838/head:pull/22838

PR: https://git.openjdk.org/jdk/pull/22838