[crac] RFR: More robust classpath parsing

[Radim Vansa]

On Windows, path with forward slashes starting with `/` is an accepted classpath element, even though it might seem as invalid and parsing in `Path.of(...)` would fail.

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Commit messages:
 - More robust classpath parsing

Changes: https://git.openjdk.org/crac/pull/140/files
 Webrev: https://webrevs.openjdk.org/?repo=crac&pr=140&range=00
  Stats: 58 lines in 2 files changed: 57 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/crac/pull/140.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/140/head:pull/140

PR: https://git.openjdk.org/crac/pull/140