[11] 2020-03-03, Bulk backports to sh/jdk11

[Aleksey Shipilev]

https://cr.openjdk.java.net/~shade/shenandoah/backports/jdk11-20200303/webrev.01/

This backports the following improvements to sh/jdk11:
 [backport] 8238851: Shenandoah: C1: Resolve into registers of correct type
 [backport] 8237837: Shenandoah: assert(mem == __null) failed: only one safepoint
 [backport] 8240215: Shenandoah: remove ShenandoahAllocationTrace
 [backport] 8240216: Shenandoah: remove ShenandoahTerminationTrace
 [backport] 8240217: Shenandoah: remove ShenandoahEvacAssist

All apply cleanly, except 8240217, where ShenandoahEvacAssist has different context. This is not a
problem, since the entire block is going away, so I purged it by hand.

Please review carefully.

Testing: hotspot_gc_shenandoah {fastdebug,release}

-- 
Thanks,
-Aleksey