When generating code for a function call, take the inferred operand type into account

When generating code for a function call, take the inferred operand type into account. If we don't do this, the Java code we generate for CONCAT(CAST(NULL AS ANY), 'x') does not compile, because the first parameter is of type Object; it needs to be String (based on the inferred operand type of VARCHAR).

We achieve this by using SqlOperator.operandTypeInference at validate time, storing the list of inferred operand types for the call, then using that list (if available) during code generation.