RFR: Add parallel worker timings for remembered set scan [v2]

[earthling-amzn]

> ### Description
> Followed the existing pattern to add parallel working timings for remembered set scan.
> 
> ### Testing
> Ran Dacapo, looks like this in the logs:
> [157.867s][202297][info] Concurrent Reset                  94013 us
> [157.867s][202297][info] Pause Init Mark (G)              579650 us
> [157.867s][202297][info] Pause Init Mark (N)              579456 us
> [157.867s][202297][info]   Scan Remembered Set            483166 us, parallelism: 3.91x
> [157.867s][202297][info]     RS: <total>                 1891580 us
> [157.867s][202297][info]     RS: Scan Clusters           1891580 us, workers (us): 481972, 468615, 457912, 483081, 
> [157.867s][202297][info]   Update Region States               78 us
> [157.867s][202297][info] Concurrent Mark Roots             18932 us, parallelism: 1.98x

earthling-amzn has updated the pull request incrementally with two additional commits since the last revision:

 - Align '*' to type, not variable
 - Revert unrelated whitespace change.

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

Changes:
  - all: https://git.openjdk.java.net/shenandoah/pull/27/files
  - new: https://git.openjdk.java.net/shenandoah/pull/27/files/9cc042c8..123c59ec

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=27&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=27&range=00-01

  Stats: 9 lines in 2 files changed: 0 ins; 0 del; 9 mod
  Patch: https://git.openjdk.java.net/shenandoah/pull/27.diff
  Fetch: git fetch https://git.openjdk.java.net/shenandoah pull/27/head:pull/27

PR: https://git.openjdk.java.net/shenandoah/pull/27