RFR: 8351142: Add JFR monitor deflation and statistics events

[Aleksey Shipilev]

We already have JFR JavaMonitorInflate event, which tells when the monitor is inflated. We are missing JavaMonitorDeflate event, which would tell us when the monitor is deflated. This makes it hard to see the monitor lifecycle, and/or estimate the population of currently inflated monitors. I believe we should add JavaMonitorDeflate event. It would also be useful to have the statistics for the number of currently used/deflating monitors. Deflation event alone would require post-processing to investigate this, so it would be good to have the statistics event as well.

This would also replace two of the RT counters that are going away in [JDK-8348829](https://bugs.openjdk.org/browse/JDK-8348829).

Monitor deflation is done asynchronously in `MonitorDeflationThread`, so the additional overhead of recording the deflation events would likely be performance neutral. We still only enable the statistics event by default to be on a safer side.

Additional testing:
 - [x] Linux x86_64 server fastdebug, `jdk_jfr`

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Commit messages:
 - Separate statistics event as well
 - Fix

Changes: https://git.openjdk.org/jdk/pull/23900/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23900&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8351142
  Stats: 267 lines in 8 files changed: 267 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/23900.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23900/head:pull/23900

PR: https://git.openjdk.org/jdk/pull/23900