RFR: 8257234 : Add gz option to SA jmap to write a gzipped heap dump [v5]

[Lin Zang]

> 8257234 : Add gz option to SA jmap to write a gzipped heap dump

Lin Zang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Merge branch 'master' into sa
 - refine segment heap dump
 - delete unnecessary print
 - refine comments
 - 8257234 : Add gz option to SA jmap to write a gzipped heap dump

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1712/files
  - new: https://git.openjdk.java.net/jdk/pull/1712/files/e7b53589..c720aca2

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1712&range=04
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1712&range=03-04

  Stats: 99272 lines in 2659 files changed: 49749 ins; 30327 del; 19196 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1712.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1712/head:pull/1712

PR: https://git.openjdk.java.net/jdk/pull/1712