RFR: JDK-8300245: Replace NULL with nullptr in share/jfr/

[Johan Sjölen]

Do the conversion in the share/jfr/ sub-directory and all of its files.

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Commit messages:
 - More manual fixes
 - Merge remote-tracking branch 'origin/master' into JDK-8300245
 - Manual fixes
 -  Replace NULL with nullptr in share/jfr/

Changes: https://git.openjdk.org/jdk/pull/12034/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12034&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300245
  Stats: 2079 lines in 126 files changed: 0 ins; 0 del; 2079 mod
  Patch: https://git.openjdk.org/jdk/pull/12034.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12034/head:pull/12034

PR: https://git.openjdk.org/jdk/pull/12034