RFR: 8375643: G1: Convert G1RegionMarkStatsCache to use Atomic<T> [v2]

[Thomas Schatzl]

> Hi all,
> 
>   please review this change to make `G1RegionMarkStatsCache` use `Atomic<T>`.
> 
> The only unusual part is that I added two getters to that class to avoid the repeated `.load_relaxed()` typing.
> 
> Testing: gha
> 
> Thanks,
>   Thomas

Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:

  * shade review

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/29303/files
  - new: https://git.openjdk.org/jdk/pull/29303/files/3929f90b..13264bf3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29303&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29303&range=00-01

  Stats: 4 lines in 1 file changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/29303.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29303/head:pull/29303

PR: https://git.openjdk.org/jdk/pull/29303