RFR: 8307615: Linker::nativeLinker should not be restricted (mainline)

[Maurizio Cimadamore]

Port of: https://git.openjdk.org/panama-foreign/pull/831

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Commit messages:
 - Cleanup code so that restricted method check is shared
 - Initial push

Changes: https://git.openjdk.org/jdk/pull/13863/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13863&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307615
  Stats: 128 lines in 11 files changed: 65 ins; 17 del; 46 mod
  Patch: https://git.openjdk.org/jdk/pull/13863.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13863/head:pull/13863

PR: https://git.openjdk.org/jdk/pull/13863