RFR: 8364169: (NMT) Move nativeCallStack to nmt

[Thomas Stuefe]

Trivial file move of NativeCallStack to the `nmt` sub directory.

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Commit messages:
 - start

Changes: https://git.openjdk.org/jdk/pull/26498/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26498&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8364169
  Stats: 54 lines in 21 files changed: 20 ins; 20 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/26498.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26498/head:pull/26498

PR: https://git.openjdk.org/jdk/pull/26498