RFR: 8247918: Clarify Reader.skip behavior for end of stream [v3]

[Brian Burkhalter]

> Please review this clarification of the specification of the method `skip(long)` in `java.io.Reader` and its subclasses. Specifically, the behavior of the method is made clear for the case when the `Reader` is already at the end of its stream when the method is invoked. A corresponding CSR will be filed. Also, the change includes an update to an existing test in order to verify that the specification change reflects actual behavior.

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

  8247918: Remove verbiage describing impossible behavior in CharArrayReader and StringReader

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2274/files
  - new: https://git.openjdk.java.net/jdk/pull/2274/files/2a2ceb41..a33245d3

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2274&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2274&range=01-02

  Stats: 17 lines in 2 files changed: 15 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2274.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2274/head:pull/2274

PR: https://git.openjdk.java.net/jdk/pull/2274