RFR: 8338534: GenShen: Handle alloc failure differently when immediate garbage is pending

[Kelvin Nilsen]

Several changes are implemented here:

1. Re-order the phases that execute immediately after final-mark so that we do concurrent-cleanup quicker (but still after concurrent weak references)
2. After immediate garbage has been reclaimed by concurrent cleanup, notify waiting allocators
3. If an allocation failure occurs while immediate garbage recycling is pending, stall the allocation but do not cancel the concurrent gc.

-------------

Commit messages:
 - Fix whitespace
 - Experiment with white space jcheck
 - Whitespace
 - Do not cancel GC on allocation failure if immediate garbage is adequate
 - Improve comments regarding when we can recycle trashed regions
 - Do not clear alloc-failure flag after cleanup early
 - Notify waiting allocators after cleanup of immediate garbage
 - Do not log_status() for free set after cleanup early
 - Reorder concurrent cleanup following final mark
 - Merge branch 'openjdk:master' into master
 - ... and 19 more: https://git.openjdk.org/shenandoah/compare/7cc63abc...f11a3c81

Changes: https://git.openjdk.org/shenandoah/pull/479/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=479&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338534
  Stats: 73 lines in 8 files changed: 48 ins; 6 del; 19 mod
  Patch: https://git.openjdk.org/shenandoah/pull/479.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/479/head:pull/479

PR: https://git.openjdk.org/shenandoah/pull/479