RFR: 8351142: Add JFR monitor deflation and statistics events [v2]

[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`

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:

 - Merge branch 'master' into JDK-8351142-jfr-deflate-event
 - Test updates
 - Rework statistics event to be actually statistics
 - Filter JFR HiddenWait consistently
 - Event metadata touchups
 - Separate statistics event as well
 - Fix

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/23900/files
  - new: https://git.openjdk.org/jdk/pull/23900/files/0cbb9f53..8102aed8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23900&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23900&range=00-01

  Stats: 5427 lines in 140 files changed: 3043 ins; 1350 del; 1034 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