RFR [11u]: Bulk backports to sh/jdk11

[Aleksey Shipilev]

Pick up another batch of simple sh/jdk11 backports:
 [backport] 8220664: Simplify ShenandoahUpdateHeapRefsClosure
 [backport] 8222403: Shenandoah: Remove ShenandoahAlwaysTrueClosure, use AlwaysTrueClosure instead
 [backport] 8222425: Shenandoah: Move commonly used closures to separate files
 [backport] 8222843: Print Shenandoah cset map addresses in hs_err
 [backport] 8222838: Shenandoah: SEGV on accessing cset bitmap for NULL ptr

Webrev:
  http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk11-20190426/webrev.01/

Testing: hotspot_gc_shenandoah {fastdebug,release}

-- 
Thanks,
-Aleksey