RFR: 8352624: Add missing {@code} to PassFailJFrame.Builder.splitUI

[Alexey Ivanov]

A trivial fix to add `{@code}` to the description of `splitUI` methods in `PassFailJFrame.Builder`.

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Commit messages:
 - 8352624: Add missing {@code} to PassFailJFrame.Builder.splitUI

Changes: https://git.openjdk.org/jdk/pull/24235/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24235&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/jdk/pull/24235.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24235/head:pull/24235

PR: https://git.openjdk.org/jdk/pull/24235