Overhaul actuator endpoint code

Refactor several areas of the actuator endpoint code in order to make
future extensions easier. The primary goal is to introduce the concept
of an `ExposableEndpoint` that has technology specific subclasses and
can carry additional data for filters to use. Many other changes have
been made along the way including:

* A new EndpointSupplier interface that allows cleaner separation of
  supplying vs discovering endpoints. This allows cleaner class names
  and allows for better auto-configuration since a user can choose to
  provide their own supplier entirely.

* A `DiscoveredEndpoint` interface that allows the `EndpointFilter`
  to be greatly simplified. A filter now doesn't need to know about
  discovery concerns unless absolutely necessary.

* Improved naming and package structure. Many technology specific
  concerns are now grouped in a better way. Related concerns are
  co-located and concepts from one area no longer leakage into another.

* Simplified `HandlerMapping` implementations. Many common concerns have
  been pulled up helping to create simpler subclasses.

* Simplified JMX adapters. Many of the intermediary `Info` classes have
  been removed. The `DiscoveredJmxOperation` is now responsible for
  mapping methods to operations.

* A specific @`HealthEndpointCloudFoundryExtension` for Cloud Foundry.
  The extension logic used to create a "full" health endpoint extension
  has been made explicit.

Fixes gh-11428
Fixes gh-11581

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/endpoint/web/EndpointMapping.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -37,6 +37,18 @@ public class EndpointMapping {
 		this.path = normalizePath(path);
 	}
 
+	/**
+	 * Returns the path to which endpoints should be mapped.
+	 * @return the path
+	 */
+	public String getPath() {
+		return this.path;
+	}
+
+	public String createSubPath(String path) {
+		return this.path + normalizePath(path);
+	}
+
 	private static String normalizePath(String path) {
 		if (!StringUtils.hasText(path)) {
 			return path;
@@ -51,16 +63,4 @@ public class EndpointMapping {
 		return normalizedPath;
 	}
 
-	/**
-	 * Returns the path to which endpoints should be mapped.
-	 * @return the path
-	 */
-	public String getPath() {
-		return this.path;
-	}
-
-	public String createSubPath(String path) {
-		return this.path + normalizePath(path);
-	}
-
 }