RFR 8226310: Shenandoah: Concurrent evacuation of CLDG

[Zhengyu Gu]

Please review this patch that moves evacuation of CLDG to concurrent phase.


Bug: https://bugs.openjdk.java.net/browse/JDK-8226310
Webrev: http://cr.openjdk.java.net/~zgu/JDK-8226310/webrev.00/

Test:
   hotspot_gc_shenandoah (fastdebug and release)

Thanks,

-Zhengyu