DERBY-1576: Extend the CASE expression syntax for "simple case"

Implement simple case as described by the SQL:1999 standard, including the
SQL:2003 extension F262 "Extended CASE expression", and the SQL:2011
extension F263 "Comma-separated predicates in simple CASE expression".

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1595778 13f79535-47bb-0310-9956-ffa450edef68