[jdk21u-dev] RFR: 8325456: Rename nsk_mutex.h

[Goetz Lindenmaier]

I backport this ot make later backports clean.

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Commit messages:
 - Backport 10beb3184e14e2714cd836029680a8b2d3fd5011

Changes: https://git.openjdk.org/jdk21u-dev/pull/1765/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1765&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325456
  Stats: 4 lines in 2 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1765.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1765/head:pull/1765

PR: https://git.openjdk.org/jdk21u-dev/pull/1765