RFR: 8256011: Shenandoah: Don't resurrect finalizably reachable objects [v2]

[Roman Kennke]

> In the weak-LRB we currently return referents when it is 'marked', that is when it's either reachable strongly or through a finalizable object. This means a finalizable object can be resurrected by Reference.get(), which is wrong. Only truly strongly reachable objects should be returned by Reference.get() during weak-reference-processing. 
> 
> Testing: hotspot_gc_shenandoah, tier1 & tier2 with -XX:+UseShenandoahGC

Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:

  Simplify condition, don't resurrect finalizably reachable objects even on phantom access

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1109/files
  - new: https://git.openjdk.java.net/jdk/pull/1109/files/672333cc..189be782

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1109&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1109&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1109.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1109/head:pull/1109

PR: https://git.openjdk.java.net/jdk/pull/1109