[jdk21u] RFR: 8316514: Better diagnostic header for VtableStub

[Aleksey Shipilev]

Clean backport to improve diagnostic logging.

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Commit messages:
 - Backport 6c61bc195090abf73683b811e214810a1226d299

Changes: https://git.openjdk.org/jdk21u/pull/198/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=198&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316514
  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk21u/pull/198.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/198/head:pull/198

PR: https://git.openjdk.org/jdk21u/pull/198