RFR: 8345773: Class-File API debug printing capability

[Adam Sotona]

Class-File API lost debug printing capability with removal of the `j.l.classfile.components.ClassPrinter` in JDK-8345343.
This PR adds `j.l.classfile.CompoundElement::toDebugString` method to restore the capability.

Please review.

Thank you,
Adam

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Commit messages:
 - unused import
 - 8345773: Class-File API debug printing capability

Changes: https://git.openjdk.org/jdk/pull/22634/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22634&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345773
  Stats: 53 lines in 3 files changed: 29 ins; 1 del; 23 mod
  Patch: https://git.openjdk.org/jdk/pull/22634.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22634/head:pull/22634

PR: https://git.openjdk.org/jdk/pull/22634