RFR: 8287818: Shenandoah: adapt nmethod arming from Loom [v2]

[Zhengyu Gu]

> Loom implemented nmethod arming mechanism, which is very similar to Shenandoah's. Shenandoah can use it.
> 
> Test:
> 
> - [x] hotspot_gc_shenandoah on Linux x86_64 and Windows x64
> - [x] tier1 with Shenandoah GC on Linux x86_64 and Windows x64 
> - [x] hotspot_gc_shenandoah on AArch64

Zhengyu Gu has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Add a newline
 - Merge branch 'master' into 8287818-nmethod-arming
 - 8287818: Shenandoah: adapt nmethod arming from Loom
 - Merge branch 'master' into migrate_nmethod_arming_shenandoah
 - v0

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/9048/files
  - new: https://git.openjdk.org/jdk/pull/9048/files/30a2f41b..b4ef6d63

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9048&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9048&range=00-01

  Stats: 64264 lines in 1573 files changed: 35422 ins; 15195 del; 13647 mod
  Patch: https://git.openjdk.org/jdk/pull/9048.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9048/head:pull/9048

PR: https://git.openjdk.org/jdk/pull/9048