[jdk21u-dev] RFR: 8323803: ConstantOopReadValue::print_on should print 'null' instead of 'nullptr'

[Daniel Hu]

Clean backport. Fixes ConstantOopReadValue::print_on printing 'nullptr' when it should print 'null'; this is a regression from [JDK-8300242](https://bugs.openjdk.org/browse/JDK-8300242) introduced in 21-ga https://github.com/openjdk/jdk/commit/cfe57466ddecb93b528478d0b053b089dd1ed285. GHA passes.

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Commit messages:
 - Backport 7620b129888d57514d9ef588e0681f1d43377236

Changes: https://git.openjdk.org/jdk21u-dev/pull/2345/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2345&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323803
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2345.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2345/head:pull/2345

PR: https://git.openjdk.org/jdk21u-dev/pull/2345