RFR: 4890732: GZIPOutputStream doesn't support optional GZIP fields [v4]

[Lin Zang]

> 4890732: GZIPOutputStream doesn't support optional GZIP fields

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

  add class GZIPHeaderData, refine testcases

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3072/files
  - new: https://git.openjdk.java.net/jdk/pull/3072/files/9b7dabfe..03b3e966

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3072&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3072&range=02-03

  Stats: 633 lines in 3 files changed: 421 ins; 183 del; 29 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3072.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3072/head:pull/3072

PR: https://git.openjdk.java.net/jdk/pull/3072