RFR: 8339329: ConstantPoolBuilder#constantValueEntry method doc typo and clarifications

[David M. Lloyd]

Please review this small documentation change to ConstantPoolBuilder to fix a typo and clarify the usage of the `constantValueEntry` method.

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Commit messages:
 - 8339329: ConstantPoolBuilder#constantValueEntry method doc typo and clarifications

Changes: https://git.openjdk.org/jdk/pull/20796/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20796&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339329
  Stats: 4 lines in 1 file changed: 3 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20796.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20796/head:pull/20796

PR: https://git.openjdk.org/jdk/pull/20796