RFR: 8332517: G1: Refactor G1AllocRegion [v2]

[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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge remote-tracking branch 'upstream/master' into AllocatorImpl_V2
 - init

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19902/files
  - new: https://git.openjdk.org/jdk/pull/19902/files/d2b6e457..1ec87cac

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19902&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19902&range=00-01

  Stats: 11742 lines in 328 files changed: 8187 ins; 2397 del; 1158 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