[8u] Bulk backports to sh/jdk8, 2020-12-02

[Aleksey Shipilev]

https://cr.openjdk.java.net/~shade/shenandoah/backports/jdk8u-20201202/webrev.02/

This backports the following batch of changes:
   [backport] 8252660: Shenandoah: support manageable SoftMaxHeapSize option
   [backport] 8256806: Shenandoah: optimize shenandoah/jni/TestPinnedGarbage.java test
   [backport] 8240751: Shenandoah: fold ShenandoahTracer definition

Testing: {x86_64,x86_32} hotspot_gc_shenandoah

-- 
Thanks,
-Aleksey