RFR: 8348909: [BACKOUT] Implement a better allocator for downcalls

[Jorn Vernee]

This reverts https://github.com/openjdk/jdk/pull/23142

See the JBS issue. It seems that the changes are occasionally causing heap corruption, potentially due to use after free, which occasionally results in corrupt malloc headers being caught on mac. This failure was observed once in about 500 runs of this test, so it is quite intermittent.

Backing this change out seems the easiest/safest to clear up the tier 1 failure, until we've had a chance to investigate the issue further.

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Commit messages:
 - Revert "8287788: Implement a better allocator for downcalls"

Changes: https://git.openjdk.org/jdk/pull/23391/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23391&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8348909
  Stats: 492 lines in 7 files changed: 18 ins; 472 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/23391.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23391/head:pull/23391

PR: https://git.openjdk.org/jdk/pull/23391