RFR: 8262398: Shenandoah: Disable nmethod barrier and stack watermark when running with passive mode

[Zhengyu Gu]

nmethod barrier and stack watermark allow GC not to process nmethods at GC pauses, and aim to reduce GC latency, they do not benefit STW GCs, who process nmethods at pauses anyway.

Test:

- [x] hotspot_gc_shenandoah
- [x] tier1 with -XX:+UseShenandoahGC
- [x] tier1 with -XX:+UseShenandoahGC -XX:ShenandoahGCMode=passive
- [x]  tier1 with -XX:+UseShenandoahGC -XX:ShenandoahGCMode=passive -XX:-ShenandoahDegeneratedGC

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Commit messages:
 - JDK-8262398
 - init

Changes: https://git.openjdk.java.net/jdk/pull/2727/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2727&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8262398
  Stats: 39 lines in 11 files changed: 21 ins; 0 del; 18 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2727.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2727/head:pull/2727

PR: https://git.openjdk.java.net/jdk/pull/2727