RFR: 8293122: (fs) Use file cloning in macOS version of Files::copy method [v3]

[Brian Burkhalter]

> Use BSD system call `clonefile` if possible when using `Files::copy` on macOS.

Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:

  8293122: remove volatile cloneFileNotSupported; unlink target on failure; remove getattrlist

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Changes:
  - all: https://git.openjdk.org/jdk/pull/10188/files
  - new: https://git.openjdk.org/jdk/pull/10188/files/a7917d22..f51cd186

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10188&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10188&range=01-02

  Stats: 80 lines in 4 files changed: 6 ins; 69 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/10188.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10188/head:pull/10188

PR: https://git.openjdk.org/jdk/pull/10188