RFR: 8351415: (fs) Path::toAbsolutePath should specify if an absolute path has a root component

[Brian Burkhalter]

Add a sentence to the specification of `Path::toAbsolutePath` indicating that the root component of the absolute path derived from a `Path` associated with the default provider is non-`null`.

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Commit messages:
 - 8351415: (fs) Path::toAbsolutePath should specify if an absolute path has a root component

Changes: https://git.openjdk.org/jdk/pull/25161/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25161&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8351415
  Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/25161.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25161/head:pull/25161

PR: https://git.openjdk.org/jdk/pull/25161