[crac] RFR: JDK-8349365: Handle javaagent adding jars to boostrap/system classpath

[Radim Vansa]

File descriptors owned by `ClassPathEntry` in `ClassLoader` are ignored during checkpoint.

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Commit messages:
 - JDK-8349365: Handle javaagent adding jars to boostrap/system classpath

Changes: https://git.openjdk.org/crac/pull/201/files
  Webrev: https://webrevs.openjdk.org/?repo=crac&pr=201&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8349365
  Stats: 147 lines in 8 files changed: 147 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/crac/pull/201.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/201/head:pull/201

PR: https://git.openjdk.org/crac/pull/201