Introduce @CheckReturnValue annotation

This commit introduces a `@CheckReturnValue` annotation,
inspired from org.jetbrains.annotations.CheckReturnValue,
that specifies that the method return value must be used.

See spring-projectsgh-33818

spring-core/src/main/java/org/springframework/lang/CheckReturnValue.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2002-2024 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.lang;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Target;
+
+/**
+ * Specifies that the method return value must be used.
+ *
+ * <p>Inspired from {@code org.jetbrains.annotations.CheckReturnValue}, this variant
+ * has been introduce in the {@code org.springframework.lang} package to avoid
+ * requiring an extra dependency, while still following similar semantics.
+ *
+ * <p>This annotation should not be used if the return value of the method
+ * provides only <i>additional</i> information. For example, the main purpose
+ * of {@link java.util.Collection#add(Object)} is to modify the collection
+ * and the return value is only interesting when adding an element to a set,
+ * to see if the set already contained that element before.
+ *
+ * @author Sebastien Deleuze
+ * @since 6.2
+ */
+@Documented
+@Target(ElementType.METHOD)
+public @interface CheckReturnValue {
+}