RFR: 8269293: ObjectMonitor thread id fields should be 64 bits.

[Coleen Phillimore]

This is a trivial change to fix the type of _previous_version_tid and _notifier_tid in ObjectMonitor to be unint64_t.
Tested with tier1-3 and JFR tests on linux-x64-debug and windows-x64-debug.  I don't have a 32 bit system to test this out on.

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Commit messages:
 - 8269293: ObjectMonitor thread id fields should be 64 bits.

Changes: https://git.openjdk.java.net/jdk/pull/4584/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4584&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8269293
  Stats: 5 lines in 2 files changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4584.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4584/head:pull/4584

PR: https://git.openjdk.java.net/jdk/pull/4584