RFR: JDK-8319626: Override toString() for ZipFile

[Justin Lu]

Please review this PR and [CSR](https://bugs.openjdk.org/browse/JDK-8319982) which overrides and provides an implementation of `toString()` in _java.util.zip.ZipFile_ (and by extension, _java.util.jar.JarFile_).

This change is primarily to provide a more informative String representation of the two classes rather than the default hexadecimal representation of the hash code.

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Commit messages:
 - init

Changes: https://git.openjdk.org/jdk/pull/16643/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16643&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319626
  Stats: 13 lines in 1 file changed: 13 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/16643.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16643/head:pull/16643

PR: https://git.openjdk.org/jdk/pull/16643