RFR: 8257234 : Add gz option to SA jmap to write a gzipped heap dump [v15]

[Lin Zang]

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

Lin Zang has updated the pull request incrementally with one additional commit since the last revision:

  refine help message and also refactor the logic in CommandProcessor

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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/0d30aaf3..0aa703d3

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1712&range=14
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1712&range=13-14

  Stats: 55 lines in 3 files changed: 10 ins; 16 del; 29 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