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

[Roman Kennke]

> 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

Looks good, thanks!

Roman