Introduce a NativeDetector utility class

With the introduction of the -H:+InlineBeforeAnalysis native image
compiler flag in GraalVM 21.0.0, it is now possible to use an utility method and get code
removal at build time.

This flag will be enabled as of Spring Native 0.9.0.

closes gh-25795

spring-aop/src/main/java/org/springframework/aop/framework/DefaultAopProxyFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -20,6 +20,7 @@ import java.io.Serializable;
 import java.lang.reflect.Proxy;
 
 import org.springframework.aop.SpringProxy;
+import org.springframework.core.NativeDetector;
 
 /**
  * Default {@link AopProxyFactory} implementation, creating either a CGLIB proxy
@@ -47,17 +48,10 @@ import org.springframework.aop.SpringProxy;
 @SuppressWarnings("serial")
 public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {
 
-	/**
-	 * Whether this environment lives within a native image.
-	 * Exposed as a private static field rather than in a {@code NativeImageDetector.inNativeImage()} static method due to https://github.com/oracle/graal/issues/2594.
-	 * @see <a href="https://github.com/oracle/graal/blob/master/sdk/src/org.graalvm.nativeimage/src/org/graalvm/nativeimage/ImageInfo.java">ImageInfo.java</a>
-	 */
-	private static final boolean IN_NATIVE_IMAGE = (System.getProperty("org.graalvm.nativeimage.imagecode") != null);
-
 
 	@Override
 	public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
-		if (!IN_NATIVE_IMAGE &&
+		if (!NativeDetector.inNativeImage() &&
 				(config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config))) {
 			Class<?> targetClass = config.getTargetClass();
 			if (targetClass == null) {