RFR: 8346568: G1: Other time can be negative

[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. Concurrent task execution time
    - Sometimes just triggering concurrent work takes 2 digit milliseconds. Changed to add only initiating time on sum_of_sub_phases and keep displaying concurrent tasks' average execution time.

Testing: tier 1 ~ 5

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Commit messages:
 - Separate measurement for cleanup

Changes: https://git.openjdk.org/jdk/pull/24454/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24454&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346568
  Stats: 61 lines in 4 files changed: 35 ins; 17 del; 9 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