RFR: 8359110: Log accumulated GC and process CPU time upon VM exit

[Jonas Norlinder]

Add support to log CPU cost for GC during VM exit with `-Xlog:gc`.


[1.500s][info ][gc] GC CPU cost: 1.75%


Additionally, detailed information may be retrieved with `-Xlog:gc=trace`


[1.500s][trace][gc] Process CPU time: 4.945370s
[1.500s][trace][gc] GC CPU time: 0.086382s
[1.500s][info ][gc] GC CPU cost: 1.75%

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Commit messages:
 - Add elapsed_process_vtime
 - Log GC vtime on VM exit

Changes: https://git.openjdk.org/jdk/pull/25779/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25779&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8359110
  Stats: 212 lines in 22 files changed: 206 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/25779.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25779/head:pull/25779

PR: https://git.openjdk.org/jdk/pull/25779