Add @FunctionalInterface to remaining public and protected interfaces

See gh-6857

spring-boot-tools/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/CustomLoaderLayout.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2016 the original author or authors.
+ * Copyright 2012-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,6 +25,7 @@ import java.io.IOException;
  * @author Phillip Webb
  * @since 1.5.0
  */
+@FunctionalInterface
 public interface CustomLoaderLayout {
 
 	/**

spring-boot-tools/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/LayoutFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2016 the original author or authors.
+ * Copyright 2012-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,6 +24,7 @@ import java.io.File;
  * @author Dave Syer
  * @author Phillip Webb
  */
+@FunctionalInterface
 public interface LayoutFactory {
 
 	/**

spring-boot-tools/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/Repackager.java

@@ -404,6 +404,7 @@ public class Repackager {
 	 * Callback interface used to present a warning when finding the main class takes too
 	 * long.
 	 */
+	@FunctionalInterface
 	public interface MainClassTimeoutWarningListener {
 
 		/**