RFR: Remaining Shenandoah backports jdk/jdk -> sh/jdk11

[Roman Kennke]

This backports the following changes to sh/jdk11:

JDK-8221751: Shenandoah: Improve SATB enqueueing
JDK-8221848: Shenandoah: ArrayCopy post-barrier improvements
JDK-8222227: Shenandoah: Fix Traversal GC weak roots handling in
final-traversal pause
JDK-8222259: Shenandoah: Pre-evacuate string-dedup roots in Traversal GC
JDK-8222188: Shenandoah: Adjust Shenandoah work gang types
JDK-8218468: Load barrier slow path node should be MachTypeNode
JDK-8223651: Build fails with --with-jvm-features=-jfr and
--disable-precompiled-headers

Changes transplanted with minimal and simple changes.
Testing: hotspot_gc_shenandoah fine

Ok?

Note: I cut out the following change:
JDK-8223570: Shenandoah needs to acquire lock before
CLDG::clear_claimed_marks

We have no ClassLoaderDataGraph_lock in jdk11, and the change made me
think that we either move the clear_claimed_marks() to the end of
init_traversal(), or look into removing it, because it should not be
necessary (it's a smell). In any case, this should be reworked in
jdk/jdk and then percolated down.

Roman