RFR: 8294399: (ch) Refactor some methods out of sun.nio.ch.UnixFileDispatcherImpl [v3]

[Brian Burkhalter]

> Interpose a new class `sun.nio.ch.UnixDispatcher` between `sun.nio.ch.NativeDispatcher` and its current subclasses `sun.nio.ch.DatagramDispatcher` and `sun.nio.ch.SocketDispatcher`; refactor some methods out of `sun.nio.ch.UnixFileDispatcherImpl` into this updated hierarchy.

Brian Burkhalter has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge
 - 8294399: Correct copyright years
 - 8294399: (ch) Refactor some methods out of sun.nio.ch.UnixFileDispatcherImpl

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Changes:
  - all: https://git.openjdk.org/jdk/pull/10434/files
  - new: https://git.openjdk.org/jdk/pull/10434/files/a16bc10a..b66ff40e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10434&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10434&range=01-02

  Stats: 172362 lines in 2322 files changed: 112715 ins; 22013 del; 37634 mod
  Patch: https://git.openjdk.org/jdk/pull/10434.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10434/head:pull/10434

PR: https://git.openjdk.org/jdk/pull/10434