RFR: 8238174: migrate ObjectMonitor::_owner field away from C++ volatile semantics

[Daniel D.Daugherty]

Drop volatile from the ObjectMonitor::_owner field. Update all naked
field loads to use the new owner_raw() accessor or the existing
owner_is_DEFLATER_MARKER() accessor.

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Commit messages:
 - 8238174: migrate ObjectMonitor::_owner field away from C++ volatile semantics

Changes: https://git.openjdk.java.net/jdk/pull/1278/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1278&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8238174
  Stats: 46 lines in 4 files changed: 5 ins; 0 del; 41 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1278.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1278/head:pull/1278

PR: https://git.openjdk.java.net/jdk/pull/1278