RFR: 8375981: G1: Convert G1RemSet helper classes to use Atomic<T> [v2]

[Thomas Schatzl]

> Hi all,
> 
>   please review this conversion of `G1RemSet` helper classes to use `Atomic<>`.
> 
> There has been one additional non-volatile member that has been converted to use `Atomic<T>`.
> 
> Testing: gha, tier1
> 
> 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/29345/files
  - new: https://git.openjdk.org/jdk/pull/29345/files/ebc28c33..9cd2c155

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29345&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29345&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/29345.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29345/head:pull/29345

PR: https://git.openjdk.org/jdk/pull/29345