RFR: 8346568: G1: Other time can be negative [v3]

[Sangheon Kim]

> Other time described in this bug is displayed at G1GCPhaseTimes::print_other(total_measured_time - sum_of_sub_phases). And the value can be negative for 3 reasons.
> 1. Different scope of measurement
>     - 3 variables is out of scope from total_measured_time. Those used for wait-root-region-scan, verify-before/after. 
>        (_root_region_scan_wait_time_ms, _cur_verify_before_time_ms and _cur_verify_after_time_ms)
>     - Changed not to be included in sum_of_sub_phases.
>     - One may want to include them in total_measured_time but I think it is better to be addressed in a separate ticket. 
> 2. Duplicated measurement
>     - Initial and optional evacuation time include nmethod-cleanup-time, so separated them as we are already measuring them. As there is no public getter, just added cleanup time when those evacuation time are used internally.
> 3. Pre Concurrent task execution time
>     - Sometimes the difference between the existing average time and pre-concurrent work is 2 digit milliseconds. Changed to measure exact time rather than accumulating the average value to sum_of_sub_phases and keep displaying concurrent tasks' average execution time.
> 
> Testing: tier 1 ~ 5

Sangheon Kim has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:

 - Review from Thomas
 - Separate measurement for cleanup

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Changes: https://git.openjdk.org/jdk/pull/24454/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24454&range=02
  Stats: 68 lines in 4 files changed: 36 ins; 20 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/24454.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24454/head:pull/24454

PR: https://git.openjdk.org/jdk/pull/24454