Add get*Names() to FunctionCatalog

We could go wit a separate interface, but it seems sensible to
keep it together really, so that callers don't have to downcast.

spring-cloud-function-context/src/main/java/org/springframework/cloud/function/context/InMemoryFunctionCatalog.java

@@ -94,4 +94,20 @@ public class InMemoryFunctionCatalog implements FunctionCatalog {
 	public <T> Consumer<T> lookupConsumer(String name) {
 		return (Consumer<T>) consumers.get(name);
 	}
+
+	@Override
+	public Set<String> getSupplierNames() {
+		return suppliers.keySet();
+	}
+
+	@Override
+	public Set<String> getFunctionNames() {
+		return functions.keySet();
+	}
+
+	@Override
+	public Set<String> getConsumerNames() {
+		return consumers.keySet();
+	}
+
 }