RFR: 8304292: Memory leak related to ClassLoader::update_class_path_entry_list

[Calvin Cheung]

Please review this small fix for `ClassPathEntry` leak when there's a duplicate entry in the app class path (`-cp`) and the `check_for_duplicate` argument is set to `true`, the `ClassLoader::add_to_app_classpath_entries` function should delete the entry before returning. This fix also corrects the call to `update_class_path_entry_list` from `setup_app_search_path`; the `check_for_duplicate` argument should be set to `true`. Two test cases are included to exercise the code path.

Passed tiers 1 - 4 testing.

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Commit messages:
 - 8304292: Memory leak related to ClassLoader::update_class_path_entry_list

Changes: https://git.openjdk.org/jdk/pull/15132/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15132&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304292
  Stats: 65 lines in 4 files changed: 58 ins; 5 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/15132.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15132/head:pull/15132

PR: https://git.openjdk.org/jdk/pull/15132