RFR: 8253176: Signature.getParameters should specify that it can throw UnsupportedOperationException

[Valerie Peng]

This is to update the method javadoc of java.security.Signature.getParameters() with the missing `@throws UnsupportedOperationException`. In addition, the wording on the returned parameters are updated to match those in Cipher and CipherSpi classes. 

CSR will be filed later.

Thanks,
Valerie

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Commit messages:
 - 8253176: Signature.getParameters should specify that it can throw UnsupportedOperationException

Changes: https://git.openjdk.java.net/jdk/pull/8396/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8396&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253176
  Stats: 28 lines in 2 files changed: 4 ins; 3 del; 21 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8396.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8396/head:pull/8396

PR: https://git.openjdk.java.net/jdk/pull/8396