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

[Aleksey Shipilev]

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

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Thanks,
-Aleksey