RFR: 8305994: Guarantee eventual async monitor deflation [v5]

[Aleksey Shipilev]

> See discussion in the bug. This PR introduces a safety rail that kicks in when the threshold heuristics fails, and it is cleanly backportable to JDK 17, where the problem manifests as apparent memory leak. There are other options to resolve this (see the bug), but I think this one is the easiest in the interim. 
> 
> Additional testing:
>  - [x] Linux x86_64 `tier1`
>  - [x] Linux x86_64 `tier2`
>  - [x] `runtime/Monitor` tests
>  - [x] Ad-hoc experiments (see example in the bug)
>  - [x] New feature test

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  More review comments and improvements

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13474/files
  - new: https://git.openjdk.org/jdk/pull/13474/files/fb267907..6ec3b0b3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13474&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13474&range=03-04

  Stats: 172 lines in 2 files changed: 87 ins; 23 del; 62 mod
  Patch: https://git.openjdk.org/jdk/pull/13474.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13474/head:pull/13474

PR: https://git.openjdk.org/jdk/pull/13474