RFR: 6980847: (fs) Files.copy needs to be tuned [v9]

[Brian Burkhalter]

> Modify `UnixCopyFile.copyFile()` to set the transfer size to the least common multiple of the source and destination file block sizes if the block sizes are not equal. Modify `WindowsFileCopy.copy()` to set `COPY_FILE_NO_BUFFERING` in the flags passed to `CopyFileEx()` if the size of the transfer is greater than a threshold.

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

  6980847: Remove use of Files.size()

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9161/files
  - new: https://git.openjdk.org/jdk/pull/9161/files/6c7ac10c..406656e2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9161&range=08
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9161&range=07-08

  Stats: 13 lines in 1 file changed: 7 ins; 6 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/9161.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9161/head:pull/9161

PR: https://git.openjdk.org/jdk/pull/9161