RFR: 8360206: Refactor ReferenceProcessor::balance_queues [v4]

[Albert Mingkun Yang]

> Simple refactoring to clean up the inner-loop conditions and control flow. Due to the structural change, the diff is slightly large and may be harder to read than the resulting code. The new version simplifies the logic by using a single `remaining_to_move` counter in the inner loop to track remaining work, and introduces early returns to reduce indentation and improve clarity.
> 
> Test: tier1-3

Albert Mingkun Yang 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 six additional commits since the last revision:

 - Merge branch 'master' into ref-refactor
 - review
 - review
 - Merge branch 'master' into ref-refactor
 - Merge branch 'master' into ref-refactor
 - ref-refactor

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25930/files
  - new: https://git.openjdk.org/jdk/pull/25930/files/85a857e7..33a30b95

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25930&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25930&range=02-03

  Stats: 4295 lines in 200 files changed: 2546 ins; 637 del; 1112 mod
  Patch: https://git.openjdk.org/jdk/pull/25930.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25930/head:pull/25930

PR: https://git.openjdk.org/jdk/pull/25930