RFR: 8329658: Serial: Refactor ContiguousSpace::_next_compaction_space

[Guoxiong Li]

Hi all,

This patch removes the uncessary `ContiguousSpace::_next_compaction_space` and uses `DefNewGeneration::_promotion_failed` instead.

The tests `make test-tier1_gc` passed locally.

Thanks for taking the time to review.

Best Regards,
-- Guoxiong

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Commit messages:
 - JDK-8329658

Changes: https://git.openjdk.org/jdk/pull/18666/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18666&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8329658
  Stats: 36 lines in 5 files changed: 2 ins; 33 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/18666.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18666/head:pull/18666

PR: https://git.openjdk.org/jdk/pull/18666