RFR: 8369854: (ch) Refine specification of behavior of {Gathering,Writable}ByteChannel.write

[Brian Burkhalter]

Modify the specification of the `write` methods of `WritableByteChannel` and `GatheringByteChannel` in the `java.nio.channels` package to emphasize that each method invocation returns only the number of bytes written in that invocation and that `write` might have to be invoked more than once for all requested bytes to be written.

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Commit messages:
 - 8369854: (ch) Refine specification of behavior of {Gathering,Writable}ByteChannel.write

Changes: https://git.openjdk.org/jdk/pull/27833/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27833&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369854
  Stats: 16 lines in 2 files changed: 8 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/27833.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27833/head:pull/27833

PR: https://git.openjdk.org/jdk/pull/27833