RFR: 8357619: [JVMCI] Revisit phantom_ref parameter in JVMCINMethodData::get_nmethod_mirror

[Doug Simon]

The point of the `phantom_ref` parameter (introduced by [JDK-8234359](https://bugs.openjdk.org/browse/JDK-8234359)) of `JVMCINMethodData::get_nmethod_mirror` is to avoid the special resurrection semantics of a phantom read when reading the field during GC, which is when `JVMCINMethodData::invalidate_nmethod_mirror` can be called.
This case can be handled directly in `JVMCINMethodData::invalidate_nmethod_mirror` and so the `phantom_ref` parameter can be removed.

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Commit messages:
 - remove phantom_ref arg from JVMCINMethodData::get_nmethod_mirror

Changes: https://git.openjdk.org/jdk/pull/25488/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25488&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357619
  Stats: 14 lines in 3 files changed: 1 ins; 5 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/25488.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25488/head:pull/25488

PR: https://git.openjdk.org/jdk/pull/25488