RFR: 8318677: (ch) Add implNote about minBufferCap to main variant of Channels.newWriter [v2]

[Brian Burkhalter]

> Add an `implNote` about the `minBufferCap` parameter of the three-arg `Channels.newWriter` and slightly tweak the test.

Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:

  8318677: Adjust minBufferap verbiage

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16325/files
  - new: https://git.openjdk.org/jdk/pull/16325/files/5cf432fb..5f93e577

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16325&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16325&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/16325.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16325/head:pull/16325

PR: https://git.openjdk.org/jdk/pull/16325