RFR: 8320304: Refactor and simplify monitor deflation functions [v2]

[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.

Stefan Karlsson has updated the pull request incrementally with one additional commit since the last revision:

  Make classes StackObjs

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16706/files
  - new: https://git.openjdk.org/jdk/pull/16706/files/5ec4de2c..c86c7106

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16706&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16706&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 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