RFR: 8360206: Refactor ReferenceProcessor::balance_queues [v2]

[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 two additional commits since the last revision:

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

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Changes:
  - all: https://git.openjdk.org/jdk/pull/25930/files
  - new: https://git.openjdk.org/jdk/pull/25930/files/86b2df4a..3216b6ea

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25930&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25930&range=00-01

  Stats: 1713 lines in 107 files changed: 241 ins; 369 del; 1103 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