RFR: 8262398: Shenandoah: Disable nmethod barrier and stack watermark when running with passive mode [v4]

[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

Zhengyu Gu has updated the pull request incrementally with one additional commit since the last revision:

  Fix spaces

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2727/files
  - new: https://git.openjdk.java.net/jdk/pull/2727/files/2a45cb02..f9358209

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2727&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2727&range=02-03

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 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