Refine KotlinDetector for compliance with ConstantFieldFeature

After this commit, KotlinDetector#kotlinPresent is
computed at build time.

See spring-projectsgh-28624

spring-core/src/main/java/org/springframework/core/KotlinDetector.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -35,6 +35,9 @@ public abstract class KotlinDetector {
 	@Nullable
 	private static final Class<? extends Annotation> kotlinMetadata;
 
+	// For ConstantFieldFeature compliance, otherwise could be deduced from kotlinMetadata
+	private static final boolean kotlinPresent;
+
 	private static final boolean kotlinReflectPresent;
 
 	static {
@@ -48,6 +51,7 @@ public abstract class KotlinDetector {
 			metadata = null;
 		}
 		kotlinMetadata = (Class<? extends Annotation>) metadata;
+		kotlinPresent = (kotlinMetadata != null);
 		kotlinReflectPresent = ClassUtils.isPresent("kotlin.reflect.full.KClasses", classLoader);
 	}
 
@@ -56,7 +60,7 @@ public abstract class KotlinDetector {
 	 * Determine whether Kotlin is present in general.
 	 */
 	public static boolean isKotlinPresent() {
-		return (kotlinMetadata != null);
+		return kotlinPresent;
 	}
 
 	/**