RFR: JDK-8260694: (fc) Add apiNote to FileChannel.transferFrom to better describe "no bytes available" case [v2]

[Hamlin Li]

> We'd better put more detailed messages in FileChannel.transferFrom/transferTo that it will not return -1, as we met several cases where developers of framework/program assume that it will return -1 on some error conditions, e.g. EOF of src Channel of transferFrom.
> 
> please check more details in JDK-8260486, and discussion in https://mail.openjdk.java.net/pipermail/nio-dev/2021-January/008094.html

Hamlin Li has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  JDK-8260694: (fc) Add apiNote to FileChannel.transferFrom to better describe "no bytes available" case

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2329/files
  - new: https://git.openjdk.java.net/jdk/pull/2329/files/c9ed084b..91233c7f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2329&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2329&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2329.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2329/head:pull/2329

PR: https://git.openjdk.java.net/jdk/pull/2329