RFR: 8293499: Provide jmod compression level option

[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.

This change nominally requires CSR, but I would like to gauge the reaction to this patch first, before submitting a formal CSR. The interesting asymmetry against `jlink` is: `jlink` provides `--compress` option that only takes `2` for "ZIP compression". I would argue it would be beneficial to add `--compression-level` to `jlink` as well, so to select the compression level there too.

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/10213/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10213&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293499
  Stats: 99 lines in 4 files changed: 92 ins; 0 del; 7 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