[jdk11u-dev] RFR: 8234510: Remove file seeking requirement for writing a heap dump

[BuddyLiao]

Backport of the heap dump enhancement: Remove file seeking requirement for writing a heap dump

Patch did not apply cleanly, I had to resolve/modify
    src/hotspot/share/services/heapDumper.cpp

I have built it on linux x86_64 and run test-tier1

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Commit messages:
 - 8234510: Remove file seeking requirement for writing a heap dump

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/134/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=134&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8234510
  Stats: 417 lines in 1 file changed: 161 ins; 185 del; 71 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/134.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/134/head:pull/134

PR: https://git.openjdk.java.net/jdk11u-dev/pull/134