[jdk21] RFR: 8298095: Refine implSpec for SegmentAllocator

[Maurizio Cimadamore]

8298095: Refine implSpec for SegmentAllocator

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

Commit messages:
 - Backport 35b60f925a4e7e2e3f1ec7c5c1eee60206e7508a

Changes: https://git.openjdk.org/jdk21/pull/172/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21&pr=172&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8298095
  Stats: 249 lines in 1 file changed: 147 ins; 21 del; 81 mod
  Patch: https://git.openjdk.org/jdk21/pull/172.diff
  Fetch: git fetch https://git.openjdk.org/jdk21.git pull/172/head:pull/172

PR: https://git.openjdk.org/jdk21/pull/172