[8] RFR: 2020-04-20, Bulk backports to sh/jdk8

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk8u-20200420/webrev.01/

Backport window for sh/jdk8 is still closed, as we are waiting for reseed. Meanwhile, this bulk
backports the significant bunch of outstanding work. Don't be scared about the number of them: those
are either bulk removals, or a series of simple changes. That said, please review carefully.

Changes:
  [backport] 8240671: Shenandoah: refactor ShenandoahPhaseTimings
  [backport] 8240749: Shenandoah: refactor ShenandoahUtils
  [backport] 8240750: Shenandoah: remove leftover files and mentions of ShenandoahAllocTracker
  [backport] 8230853: Shenandoah: replace leftover assert(is_in(...)) with rich asserts
  [backport] 8240868: Shenandoah: remove CM-with-UR piggybacking cycles
  [backport] 8240915: Shenandoah: Remove unused fields in init mark tasks
  [backport] 8240872: Shenandoah: Avoid updating new regions from start of evacuation
  [backport] 8240873: Shenandoah: Short-cut arraycopy barriers
  [backport] 8241081: Shenandoah: Do not modify update-watermark concurrently
  [backport] 8241534: Shenandoah: region status should include update watermark
  [backport] 8240948: Shenandoah: cleanup not-forwarded-objects paths after JDK-8240868
  [backport] 8241351: Shenandoah: fragmentation metrics overhaul
  [backport] 8241435: Shenandoah: avoid disabling pacing with "aggressive"
  [backport] 8241139: Shenandoah: distribute mark-compact work exactly to minimize fragmentation
  [backport] 8241520: Shenandoah: simplify region sequence numbers handling
  [backport] 8241583: Shenandoah: turn heap lock asserts into macros
  [backport] 8241668: Shenandoah: make ShenandoahHeapRegion not derive from ContiguousSpace
  [backport] 8241673: Shenandoah: refactor anti-false-sharing padding
  [backport] 8241692: Shenandoah: remove ShenandoahHeapRegion::_reserved
  [backport] 8241743: Shenandoah: refactor and inline ShenandoahHeap::heap()
  [backport] 8241740: Shenandoah: remove ShenandoahHeapRegion::_heap
  [backport] 8241748: Shenandoah: inline MarkingContext TAMS methods
  [backport] 8241838: Shenandoah: no need to trash cset during final mark
  [backport] 8241841: Shenandoah: ditch one of allocation type counters in ShenandoahHeapRegion
  [backport] 8241842: Shenandoah: inline ShenandoahHeapRegion::region_number
  [backport] 8241844: Shenandoah: rename ShenandoahHeapRegion::region_number
  [backport] 8241845: Shenandoah: align ShenandoahHeapRegions to cache lines
  [backport] 8242267: Shenandoah: regions space needs to be aligned by os::vm_allocation_granularity()
  [backport] 8241093: Shenandoah: editorial changes in flag descriptions
  [backport] 8241926: Shenandoah: only print heap changes for operations that directly affect it
  [backport] 8241985: Shenandoah: simplify collectable garbage logging
  [backport] 8241983: Shenandoah: simplify FreeSet logging
  [backport] 8242040: Shenandoah: print allocation failure type
  [backport] 8242041: Shenandoah: adaptive heuristics should account evac reserve in free target
  [backport] 8242042: Shenandoah: tune down ShenandoahGarbageThreshold
  [backport] 8242075: Shenandoah: rename ShenandoahHeapRegionSize flag
  [backport] 8242083: Shenandoah: split "Prepare Evacuation" tracking into cset/freeset counters
  [backport] 8242089: Shenandoah: per-worker stats should be summed up, not averaged
  [backport] 8242082: Shenandoah: Purge Traversal mode
  [backport] 8242114: Shenandoah: remove ShenandoahHeapRegion::reset_alloc_metadata_to_shared
  [backport] 8242101: Shenandoah: coalesce and parallelise heap region walks during the pauses
  [backport] 8242211: Shenandoah: remove ShenandoahHeuristics::RegionData::_seqnum_last_alloc
  [backport] 8242212: Shenandoah: initialize ShenandoahHeuristics::_region_data eagerly
  [backport] 8242213: Shenandoah: remove ShenandoahHeuristics::_bytes_in_cset
  [backport] 8242227: Shenandoah: transit regions to cset state when adding to collection set
  [backport] 8242228: Shenandoah: remove unused ShenandoahCollectionSet methods

Testing: hotspot_gc_shenandoah {release, fastdebug}

-- 
Thanks,
-Aleksey