8382103: Shenandoah: Optimize ShenandoahLock size for release build

[pf0n]

The ShenandoahLock class members: _owner and shenandoah_padding(2) are only used in debug builds, but they will appear in the release build. Used ASSERT and DEBUG_ONLY macro, so they no longer appear in the release build.

Testing:

test/hotspot/jtreg/gc/shenandoah (all passed)

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Issue

• JDK-8382103: Shenandoah: Optimize ShenandoahLock size for release build (Enhancement - P5)

Reviewers

• Xiaolong Peng (@pengxiaolong - Committer)

Reviewing

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@pf0n The following labels will be automatically applied to this pull request:

• hotspot-gc
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[mlbridge]

Webrevs

• 01: Full - Incremental (6a4af6a5)
• 00: Full (3dc08a90)

[pengxiaolong]

Thanks for the cleanup！