Fix ASTERIXDB-1875 UDF in SQL++ 1. Fix the bug that if a function created with SQLPP, the callExpr in the function body is not normalzied to list input functions. 2. Fix the bug that in SQL++ Query Rewritter, the variables are not expanded before the inline the functions. 3. Add test case for this issue. 4. Make SQL++ visitor visits decorVariableExpression. 5. Optimizer test cases update.