RFR: 8256302: releasing oopStorage when deflating allows for faster deleting [v4]

[Daniel D. Daugherty]

> Releasing ObjectMonitor oopStorage earlier when deflating allows ObjectMonitor
> deletion by a JavaThread (usually the MonitorDeflationThread) to happen while a
> ThreadBlockInVM helper is in place. This should improve time-to-safepoint.

Daniel D. Daugherty has updated the pull request incrementally with one additional commit since the last revision:

  Allow ObjectMonitor::_object to be reset to nullptr when it is released which allows the code to be cleaner.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11296/files
  - new: https://git.openjdk.org/jdk/pull/11296/files/f0aad83d..958c5e95

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11296&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11296&range=02-03

  Stats: 10 lines in 4 files changed: 5 ins; 4 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11296.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/11296/head:pull/11296

PR: https://git.openjdk.org/jdk/pull/11296