RFR: 8327645: Serial heap dump should not consume double amount of disk space [v3]

[Man Cao]

> Hi all,
> 
> Could anyone review this fix to make serial heap dump only write to a single file?
> We highly appreciate the work in https://bugs.openjdk.org/browse/JDK-8306441. However, many of our customers still need to use serial heap dump, as they have limited disk space and need to dump to a network socket.
> 
> Tested:
> Stress tested with a fastdebug build with tests in `hotspot/jtreg/serviceability/dcmd/gc/HeapDump*`.
> 
> -Man

Man Cao has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:

 - Merge branch 'master' into JDK-8327645-serialdump
 - Add a variant to run serial heap dump for VThreadInHeapDump
 - Fix failure under -XX:+UseSerialGC
 - 8327645: Serial heap dump should not consume double amount of disk space

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Changes: https://git.openjdk.org/jdk/pull/18160/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18160&range=02
  Stats: 55 lines in 2 files changed: 24 ins; 0 del; 31 mod
  Patch: https://git.openjdk.org/jdk/pull/18160.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18160/head:pull/18160

PR: https://git.openjdk.org/jdk/pull/18160