8387293: Shenandoah: Improve gc+stats logging for generational mode

[shipilev]

Apparently I have missed a few cases in GenShen in JDK-8385334.

[4.982s][info][gc,stats] Concurrent Evacuation 63463 us // <--- no worker details
[4.982s][info][gc,stats] Concurrent Update Cards 238 us
[4.982s][info][gc,stats] Concurrent Update Refs Prepare 244 us
[4.982s][info][gc,stats] Concurrent Update Refs 84525 us // <--- no worker details

Now:

[3.661s][info][gc,stats] Concurrent Evacuation             36906 us with 7.58x parallelism
[3.661s][info][gc,stats]   CE: Work                       279695 us total, per worker: 36155, 36104, 36078, 35945, 35507, 33010, 32910, 33985, ---, ---, ---, ---, ---, ---, ---, ---, 
[3.661s][info][gc,stats] Concurrent Update Cards             947 us
[3.661s][info][gc,stats] Concurrent Update Refs Prepare      228 us
[3.661s][info][gc,stats] Concurrent Update Refs            63106 us with 7.86x parallelism
[3.661s][info][gc,stats]   CUR: Work                      495879 us total, per worker: 61832, 62810, 63015, 61841, 61820, 61795, 61717, 61051, ---, ---, ---, ---, ---, ---, ---, ---, 

Additional testing:

• Eyeballing the logs
• Linux x86_64 server fastdebug, hotspot_gc_shenandoah

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• JDK-8387293: Shenandoah: Improve gc+stats logging for generational mode (Enhancement - P4)

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