RFR: 8324678: Replace NULL with nullptr in HotSpot gtests

[Coleen Phillimore]

If this is sufficient, here's the change for NULL to nullptr, adjusting some obvious strings that had NULL in them maybe not all.
Tested with gtest,

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Commit messages:
 - Fix some strings
 - 8324678: Replace NULL with nullptr in HotSpot gtests

Changes: https://git.openjdk.org/jdk/pull/17577/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17577&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324678
  Stats: 562 lines in 74 files changed: 0 ins; 0 del; 562 mod
  Patch: https://git.openjdk.org/jdk/pull/17577.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17577/head:pull/17577

PR: https://git.openjdk.org/jdk/pull/17577