RFR: 8325682: Rename nsk_strace.h

[Kim Barrett]

Please review this trivial change that renames the file
test/hotspot/jtreg/vmTestbase/nsk/stress/strace/nsk_strace.hpp
to nsk_strace.hpp. and replaces uses of NULL in that file.

Testing: mach5 tier1

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Commit messages:
 - rename NULLs in nsk_strace.hpp
 - rename nsk_strace.h

Changes: https://git.openjdk.org/jdk/pull/17852/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17852&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325682
  Stats: 26 lines in 11 files changed: 0 ins; 0 del; 26 mod
  Patch: https://git.openjdk.org/jdk/pull/17852.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17852/head:pull/17852

PR: https://git.openjdk.org/jdk/pull/17852