RFR: 8324681: Replace NULL with nullptr in HotSpot jtreg test native code files

[Coleen Phillimore]

This mechanically replaces NULL with nullptr in hpp/cpp native files in test native code.  This didn't attempt to change NULL in comments or strings to just null.  If you run into this and it bothers you after this push, you can change it in a smaller patch. I didn't see any when it was scrolling by to make my script more complicated.

Ran tier1-4 testing.

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Commit messages:
 - 8324681: Replace NULL with nullptr in HotSpot jtreg test native code files

Changes: https://git.openjdk.org/jdk/pull/17593/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17593&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324681
  Stats: 8196 lines in 750 files changed: 0 ins; 7 del; 8189 mod
  Patch: https://git.openjdk.org/jdk/pull/17593.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17593/head:pull/17593

PR: https://git.openjdk.org/jdk/pull/17593