RFR: 8306483: (ch) Channels.newReader(ReadableByteChannel,Charset) refers to csName

[Brian Burkhalter]

In the specification of `Channels.newReader(ReadableByteChannel,Charset)`, change `Charset.forName(csName).newDecoder()` to `charset.newDecoder()`.

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Commit messages:
 - 8306483: (ch) Channels.newReader(ReadableByteChannel,Charset) refers to csName

Changes: https://git.openjdk.org/jdk/pull/13547/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13547&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306483
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/13547.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13547/head:pull/13547

PR: https://git.openjdk.org/jdk/pull/13547