RFR: 8332517: G1: Refactor G1AllocRegion [v3]

[Ivan Walulya]

> Hi all,
> 
> Please review this refactoring change to move `_used_bytes_before` out of the base class and into the only child class G1GCAllocRegion that requires those details.
> 
> Additionally, I removed wrapper methods that do not seem to improve readability in anyway.
> 
> Testing: Tier 1-3

Ivan Walulya has updated the pull request incrementally with one additional commit since the last revision:

  Albert review

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19902/files
  - new: https://git.openjdk.org/jdk/pull/19902/files/1ec87cac..2a0b5bf0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19902&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19902&range=01-02

  Stats: 11 lines in 2 files changed: 3 ins; 5 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/19902.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19902/head:pull/19902

PR: https://git.openjdk.org/jdk/pull/19902