RFR (M) 8232575: Shenandoah: asynchronous object/region pinning

[Aleksey Shipilev]

RFE:
  https://bugs.openjdk.java.net/browse/JDK-8232575

Current object/region pinning scheme bottlenecks on a lock, rendering some non-exceptional scenarios
quite slow. The way out is to collect critical pins atomically, and then update the region states
near the code that needs it (mostly selecting collection set). See the bug for more info.

Fix:
  https://cr.openjdk.java.net/~shade/8232575/webrev.02/

Testing: hotspot_gc_shenandoah {fastdebug,release}; tier{1,2,3} with Shenandoah; GZIP workload with
{normal, traversal} x {adaptive, aggressive}

-- 
Thanks,
-Aleksey