RFR: 8273507: Convert test/jdk/java/nio/channels/Channels/TransferTo.java to TestNG test [v8]

[Markus KARG]

> Using TestNG makes it easier to maintain and extend the unit test of ChannelInputStream::transferTo.
> 
> This change was proposed by Brian Burkhalter @blbp and requested Alan Bateman @AlanBateman.
> 
> *Note: A further test addition (testing 2GB+ transfers) will be added by me in a subsequent PR using TestNG once *this* PR is merged. This will need a while due to personal scheduling, also the topics are not necessarily related, hence there are separate PRs.*

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

 - Added code comments for private methods
   
   Signed-off-by: Markus Karg <markus at headcrashing.eu>
 - Added code comment for public method
   
   Signed-off-by: Markus Karg <markus at headcrashing.eu>

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5421/files
  - new: https://git.openjdk.java.net/jdk/pull/5421/files/54b7438b..137d1f4e

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5421&range=07
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5421&range=06-07

  Stats: 18 lines in 1 file changed: 18 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5421.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5421/head:pull/5421

PR: https://git.openjdk.java.net/jdk/pull/5421