RFR: 8346920: Serial: Support allocation in old generation when heap is almost full [v2]

[Albert Mingkun Yang]

> This PR restores the support for allocation in old-gen when heap is almost full, detected as non-empty young-gen after full gc, which was removed by mistake in [JDK-8333786](https://bugs.openjdk.org/browse/JDK-8333786). With this change, the benchmark attached to the ticket now completes in ~13 GC.
> 
> Test: tier1-5

Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:

  review

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Changes:
  - all: https://git.openjdk.org/jdk/pull/23270/files
  - new: https://git.openjdk.org/jdk/pull/23270/files/30323d46..ec3da733

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23270&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23270&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/23270.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23270/head:pull/23270

PR: https://git.openjdk.org/jdk/pull/23270