RFR: 4800398: (ch spec) Clarify Channels.newChannel(InputStream) spec

[Brian Burkhalter]

Clarify that the `ReadableByteChannel` returned by `Channels::newChannel` is in blocking mode.

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Commit messages:
 - 4800398: (ch spec) Clarify Channels.newChannel(InputStream) spec

Changes: https://git.openjdk.org/jdk/pull/14961/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14961&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-4800398
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/14961.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14961/head:pull/14961

PR: https://git.openjdk.org/jdk/pull/14961