RFR: 8369219: JNI::RegisterNatives can cause a memory leak in CodeCache

[Francesco Andreuzzi]

I propose to amend the check in `nmethod::is_cold` to allow not-entrant native `nmethod` instances to be collected during GC.

Passes tier1 and tier2 (fastdebug).

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Commit messages:
 - trigger
 - nn
 - othervm
 - stuff
 - comments and fix test
 - cc
 - fix check
 - fix and test

Changes: https://git.openjdk.org/jdk/pull/27742/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27742&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369219
  Stats: 145 lines in 3 files changed: 144 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/27742.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27742/head:pull/27742

PR: https://git.openjdk.org/jdk/pull/27742