RFR: 8286829: Shenandoah: fix Shenandoah Loom support [v2]

[Zhengyu Gu]

> Please review the patch that fixes Loom support in Shenandoah GC.
> 
> - stackChunkOop is a special oop that contains stack metadata, we need to utilize nmethod entry barrier to mark, evacuate and update stack metadata.
> - During evacuation and reference updating phase, we can not guarantee all metadata in stackChunkOop is deeply good, so I force it to take slow path for the correctness, will try to optimize it later in separate CR.
> - Shenandoah uses similar way to arm and disarm nmethod as the new mechanism introduced in JDK-8284161. We may want to migrate to it in followup CR.
> 
> Test:  
> - [x] tier1 with ShenandoahGC  (Linux x86_64 and Windows x64)
> - [x] tier2 with Shenandoah GC (Linux x86_64 and Windows x64) 
> - [x] hotspot_gc_shenandoah  on Linux x86_32
> - [x] tier1 with ShenandoahGC + Loom (Linux x86_64 and Windows x64)
> - [x] tier2 with ShenandoahGC + Loom (Linux x86_64 and Windows x64)

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

  Aleksey's comment

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8924/files
  - new: https://git.openjdk.java.net/jdk/pull/8924/files/7db9c0b8..b86b51b1

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8924&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8924&range=00-01

  Stats: 7 lines in 2 files changed: 6 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8924.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8924/head:pull/8924

PR: https://git.openjdk.java.net/jdk/pull/8924