RFR: 8320304: Refactor and simplify monitor deflation functions

[Stefan Karlsson]

The recent rewrites to remove safepointed monitor deflation allows us to simplify the monitor deflation code a bit. The code is now guaranteed to be called from the MonitorDeflationThread, which is a JavaThread, and never from the VMThread.

I would like to propose two changes to the code:
1) Remove all code that supports monitor deflation from other threads than the MonitorDeflationThread
2) Extract out the logging code so that it is easier to see the structure of the monitor deflation code

I have run minimal manual of this patch. I'd like to get some feedback on the proposal before I proceed to run more in-depth testing.

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Commit messages:
 - 8320304: Refactor and simplify monitor deflation functions

Changes: https://git.openjdk.org/jdk/pull/16706/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16706&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320304
  Stats: 260 lines in 2 files changed: 120 ins; 82 del; 58 mod
  Patch: https://git.openjdk.org/jdk/pull/16706.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16706/head:pull/16706

PR: https://git.openjdk.org/jdk/pull/16706