RFR: 8292562: (fc) Use copy_file_range in FileChannel::transferTo on Linux [v8]

[Brian Burkhalter]

> Add `copy_file_range(2)` to the native Linux implementation of `FileChannel::transferTo`.

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

  8292562: Revert to test transferTo only and constrain to Linux

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9925/files
  - new: https://git.openjdk.org/jdk/pull/9925/files/ec2ad5d5..6351c8d2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9925&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9925&range=06-07

  Stats: 21 lines in 1 file changed: 1 ins; 14 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/9925.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9925/head:pull/9925

PR: https://git.openjdk.org/jdk/pull/9925