RFR: 8359110: Log accumulated GC and process CPU time upon VM exit [v12]

[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%

Jonas Norlinder has updated the pull request incrementally with two additional commits since the last revision:

 - Update closure name
 - vtime -> cpu_time and _vm_vtime -> _vmthread_cpu_time

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/25779/files
  - new: https://git.openjdk.org/jdk/pull/25779/files/293fbe95..35a74668

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25779&range=11
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25779&range=10-11

  Stats: 234 lines in 12 files changed: 102 ins; 102 del; 30 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