RFR: 2019-08-20, bulk backports to sh/jdk11

[Aleksey Shipilev]

Let me backport these to sh/jdk11, these open up further simplifications for our upstream exposure
and testing:

 [backport] 8229350: Shenandoah does not need barriers before CreateEx
 [backport] 8229865: Use explicit #include debug.hpp for STATIC_ASSERT in
gc/shenandoah/shenandoahUtils.cpp
 [backport] 8229707: [TESTBUG] Some Shenandoah tests assume Server VM by default
 [backport] 8229416: Shenandoah: Demote or remove ShenandoahOptimize*Final optimizations
 [backport] 8229419: Shenandoah: Cleanup LRB strength selector code

Webrev:
  https://cr.openjdk.java.net/~shade/shenandoah/backports/jdk11-20190820/webrev.01/

Testing: hotspot_gc_shenandoah

-- 
Thanks,
-Aleksey