RFR: 8293499: Provide jmod --compress option [v3]

[Aleksey Shipilev]

> I have been looking into `make clean-images images` performance, and realized jmod keeps compressing files with default compression level. Tuning that toward lighter compression levels improves build performance considerably, without a heavy loss in *.jmod sizes. 
> 
> This PR allows JMOD to select the compression level. Follow-ups would use this in the build system, see #10214.
> 
> The interesting asymmetry against `jlink` is: `jlink` provides `--compress` option that only takes `2` for "ZIP compression". (Separately, we could argue if it would be beneficial to extend `--compress` to `jlink` as well, so to select the compression level there too.)

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  Adopt "--compress zip-[0-9]" as option format

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/10213/files
  - new: https://git.openjdk.org/jdk/pull/10213/files/c44ecf01..59eec8c2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10213&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10213&range=01-02

  Stats: 40 lines in 3 files changed: 16 ins; 0 del; 24 mod
  Patch: https://git.openjdk.org/jdk/pull/10213.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10213/head:pull/10213

PR: https://git.openjdk.org/jdk/pull/10213