Add "wrapper" type methods to FunctionInspector

These can be used to more reliably discover whether the user
has declared a function with flux types or "bare" POJOs. They
then pave the way to supporting single valued types in a special
way.

Also consolidate and simplify the logic in FunctionInspector

spring-cloud-function-deployer/src/main/java/org/springframework/cloud/function/deployer/FunctionExtractingFunctionCatalog.java

@@ -75,6 +75,16 @@ public class FunctionExtractingFunctionCatalog implements FunctionCatalog, Funct
 		return (Class<?>) inspect(name, "getOutputType");
 	}
 
+	@Override
+	public Class<?> getInputWrapper(String name) {
+		return (Class<?>) inspect(name, "getInputWrapper");
+	}
+
+	@Override
+	public Class<?> getOutputWrapper(String name) {
+		return (Class<?>) inspect(name, "getOutputWrapper");
+	}
+
 	@Override
 	public Object convert(String name, String value) {
 		return inspect(name, "convert");