RFR: 8274112: (fc) Tune FileChannel.transferTo()

[Brian Burkhalter]

Please consider this patch which would improve the performance of
`FileChannel.transferTo()` on macOS and Windows.

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Commit messages:
 - 8274112: (fc) Tune FileChannel.transferTo()

Changes: https://git.openjdk.java.net/jdk/pull/5623/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5623&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274112
  Stats: 122 lines in 5 files changed: 108 ins; 0 del; 14 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5623.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5623/head:pull/5623

PR: https://git.openjdk.java.net/jdk/pull/5623