RFR/RFC: Shenandoah integration 2021-03-11

[Aleksey Shipilev]

Hi,

I would like to integrate the regular update of Shenandoah 8u to our integration repository, 
aarch64-port/jdk8u-shenandoah. It comes with a few large features:
  - Self-fixing load barriers
  - JFR events support
  - ShenadnoahSoftMaxHeapSize support
  - Other cleanups and bugfixes

Webrev:
   https://cr.openjdk.java.net/~shade/shenandoah/merges/aarch64-port-8u-20210311/webrev.01/

There is no merge changeset, as shenandoah/jdk8 forest is clean downstream of integration 
repository. I am tagging the whole thing as aarch64-shenandoah-jdk8u292-b05-shenandoah-merge-2021-03-11.

Testing: hotspot_gc_shenandoah; it also runs pretty stably in our CIs, and we have no user 
bugreports from our 8u nightlies

-- 
Thanks,
-Aleksey