RFR: 8340307: Add explanation around MemorySegment:reinterpret regarding arenas

[Per Minborg]

This PR proposes to add a small text segment on the `MemorySegment::reinterpret` overloads that takes an Arena stating the responsibility of actually freeing reinterpreted segments lies with the *original* arena.

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Commit messages:
 - Add doc on original arena is responsible for freeing a segment

Changes: https://git.openjdk.org/jdk/pull/21761/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21761&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340307
  Stats: 23 lines in 2 files changed: 21 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/21761.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21761/head:pull/21761

PR: https://git.openjdk.org/jdk/pull/21761