[jdk21u-dev] RFR: 8352624: Add missing {@code} to PassFailJFrame.Builder.splitUI

[Goetz Lindenmaier]

I backport this for parity with 21.0.9-oracle.

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Commit messages:
 - Backport 41f3eea9b2b7bd74d5f125dedfe107ab5b0bed26

Changes: https://git.openjdk.org/jdk21u-dev/pull/1947/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1947&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8352624
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1947.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1947/head:pull/1947

PR: https://git.openjdk.org/jdk21u-dev/pull/1947