RFR: 8286814: Shenandoah: RedefineRunningMethods.java test failed with Loom

[Zhengyu Gu]

Please review this patch that fixed failed tests.

To determine if a barrier is needed for newly allocated `stackChunkOop`, it needs to consider current GC phases, as TAMS and update watermark are specific to corresponding GC phase.

Test:

- [x] tier1 with `--enable-preview -XX:+UseShenandoahGC` on Linux x86_64 
- [x] tier2 with `--enable-preview -XX:+UseShenandoahGC` on Linux x86_64

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Commit messages:
 - Add comments
 - v0

Changes: https://git.openjdk.java.net/jdk/pull/8757/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8757&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286814
  Stats: 17 lines in 2 files changed: 9 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8757.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8757/head:pull/8757

PR: https://git.openjdk.java.net/jdk/pull/8757