RFR: 8314021: HeapDump: Optimize segmented heap file merging phase

[Yi Yang]

This patch reduce ~16%(24s->20s) time during segmented heap file merging phase and fixes a memory leak of compressor

You might argue why this is Linux-only optimization, because sendfile requires at least socket fd in other platforms([aix sendfile](https://www.ibm.com/docs/en/aix/7.1?topic=s-send-file-subroutine) [maxos sendfile](https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man2/sendfile.2.html) [win32 TransmitFile](https://learn.microsoft.com/en-us/windows/win32/api/mswsock/nf-mswsock-transmitfile)), while [only Linux](https://man7.org/linux/man-pages/man2/sendfile.2.html) supports both two file descriptors.

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Commit messages:
 - 8314021: HeapDump: Optimize segmented heap file merging phase

Changes: https://git.openjdk.org/jdk/pull/15245/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15245&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314021
  Stats: 86 lines in 4 files changed: 78 ins; 5 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/15245.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15245/head:pull/15245

PR: https://git.openjdk.org/jdk/pull/15245