RFR: JDK-8319053: Segment dump files remain after parallel heap dump on Windows

[Alex Menkov]

Segment file is closed from DumpWriter dtor.
On Unix systems `remove` can delete an opened file, on Windows it fails with "access denied".
The fix destroys DumpWriter objects for segment files after all data are dumped

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Commit messages:
 - jcheck
 - fix
 - fix

Changes: https://git.openjdk.org/jdk/pull/16462/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16462&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319053
  Stats: 22 lines in 2 files changed: 17 ins; 2 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/16462.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16462/head:pull/16462

PR: https://git.openjdk.org/jdk/pull/16462