RFR: 8351484: Race condition in max stats in MonitorList::add [v2]

[Aleksey Shipilev]

> See bug for the description of the race. New gtest test case reliably catches fire on my 5950X desktop without this fix.
> 
> I needed to add the proper constructor for `MonitorList` to make it testable. In our regular code, it is statically allocated, so its fields are implicitly initialized.
> 
> I also made counter updates `_relaxed` for completeness.
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, new test now passes
>  - [x] GHA

Aleksey Shipilev has updated the pull request incrementally with two additional commits since the last revision:

 - Can check <=
 - Object handle

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/23961/files
  - new: https://git.openjdk.org/jdk/pull/23961/files/5625984d..c3cb9fea

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23961&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23961&range=00-01

  Stats: 5 lines in 2 files changed: 3 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/23961.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23961/head:pull/23961

PR: https://git.openjdk.org/jdk/pull/23961