RFR: 8269470: Add truncation and compression information to EventHeapDump

[Denghui Dong]

Could I have a review of this change that adds the truncation and compression information to EventHeapDump?

We occasionally receive feedback from users that the heap size parsed from the heap dump does not match the GC log. We think this may be caused by the truncation of the heap dump.

So it would be nice to add truncation info to the EventHeapDump.

Also, this patch adds the compression info which is trivial to add.

Regards,
Denghui

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Commit messages:
 - 8269470: Add truncation and compression information to EventHeapDump

Changes: https://git.openjdk.java.net/jdk/pull/4608/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4608&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8269470
  Stats: 41 lines in 3 files changed: 29 ins; 6 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4608.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4608/head:pull/4608

PR: https://git.openjdk.java.net/jdk/pull/4608