[8] 2020-06-03, Bulk backports to sh/jdk8

[Aleksey Shipilev]

https://cr.openjdk.java.net/~shade/shenandoah/backports/jdk8u-20200603/webrev.01/

This backports two bugfixes:
  [backport] 8246162: Shenandoah: full GC does not mark code roots when class unloading is off
  [backport] 8245757: Shenandoah: AlwaysPreTouch should not disable heap resizing or uncommits

Testing: hotspot_gc_shenandoah {fastdebug,release}

-- 
Thanks,
-Aleksey