RFR: 8365122: G1: Minor clean up of G1SurvivorRegions [v2]

[Thomas Schatzl]

> Hi all,
> 
>   please review this small cleanup around `G1SurvivorRegions`:
> 
> - make the `_regions` member a direct member of the class
> - use the C++ for-each construct for iterating over `_regions` makes the code more readable
> 
> Testing: gha
> 
> Thanks,
>   Thomas

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

  * add growablearray include

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26692/files
  - new: https://git.openjdk.org/jdk/pull/26692/files/b73da8fc..16244cad

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26692&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26692&range=00-01

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/26692.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26692/head:pull/26692

PR: https://git.openjdk.org/jdk/pull/26692