RFR: 2020-05-15, Bulk backports to sh/jdk11

[Roman Kennke]

Looks good to me, thanks!

Roman


> https://cr.openjdk.java.net/~shade/shenandoah/backports/jdk11-20200515/webrev.01/
> 
> This backports a few leftover changes:
>  [backport] 8244730: Shenandoah: gc/shenandoah/options/TestHeuristicsUnlock.java should only...
>  [backport] 8244732: Shenandoah: move heuristics code to gc/shenandoah/heuristics
>  [backport] 8244737: Shenandoah: move mode code to gc/shenandoah/mode
>  [backport] 8244739: Shenandoah: break superclass dependency on ShenandoahNormalMode
>  [backport] 8244740: Shenandoah: rename ShenandoahNormalMode to ShenandoahSATBMode
>  [backport] 8241062: Shenandoah: rich asserts trigger "empty statement" inspection
>  [backport] 8224529: [TESTBUG] JFR TestShenandoahHeapRegion* tests fail on build w/o Shenandoah
> 
> Testing: hotspot_gc_shenandoah {fastdebug,release}, tier{1,2} with Shenandoah
>