RFR: 8278268 - (ch) InputStream returned by Channels.newInputStream should have fast path for FileChannel targets [v16]

[Markus KARG]

> This sub-issue defines the work to be done to implement JDK-8265891 solely for the particular case of FileChannel.transferFrom(ReadableByteChannel), including special treatment of SelectableByteChannel.

Markus KARG has updated the pull request incrementally with three additional commits since the last revision:

 - separate test class for each large file test
 - Base class only contains utilities and helpers
 - Renamed AbstractTransferTo to TransferToBase as it is not abstract

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6711/files
  - new: https://git.openjdk.java.net/jdk/pull/6711/files/9ae35561..c79fc0b1

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6711&range=15
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6711&range=14-15

  Stats: 725 lines in 6 files changed: 402 ins; 263 del; 60 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6711.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6711/head:pull/6711

PR: https://git.openjdk.java.net/jdk/pull/6711