RFR: JDK-8278953: Clarify Class.getDeclaredConstructor specification

[Joe Darcy]

Cleanup and regularization of the specs of the four get[Declared]Constructor[s] methods.

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Commit messages:
 - JDK-8278953: Clarify Class.getDeclaredConstructor specification

Changes: https://git.openjdk.java.net/jdk/pull/6897/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6897&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278953
  Stats: 20 lines in 1 file changed: 11 ins; 4 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6897.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6897/head:pull/6897

PR: https://git.openjdk.java.net/jdk/pull/6897