RFR: 8356127: (fs) UnixFileSystemProvider.implDelete could save a syscall in some cases

[Brian Burkhalter]

Modify `UnixFileSystemProvider.implDelete` to attempt first to delete the file using `unlink` and, if that fails, fall back to using `rmdir` if the file is a directory.

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Commit messages:
 - 8356127: (fs) UnixFileSystemProvider.implDelete could save a syscall in some cases

Changes: https://git.openjdk.org/jdk/pull/25107/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25107&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8356127
  Stats: 21 lines in 1 file changed: 13 ins; 3 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/25107.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25107/head:pull/25107

PR: https://git.openjdk.org/jdk/pull/25107