Support nested annotations in ASM-based processing again

Spring Framework 5.0 introduced a regression in ASM-based annotation
processing. Specifically, nested annotations were no longer supported,
and component scanning resulted in an exception if a candidate
component was annotated with an annotation that contained nested
annotations.

This commit fixes this regression by introducing special handling in
AnnotationTypeMapping that supports extracting values from objects of
type TypeMappedAnnotation when necessary.

Closes gh-24375

spring-context/src/test/java/example/gh24375/AnnotatedComponent.java

@@ -0,0 +1,24 @@
+/*
+ * Copyright 2002-2020 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 example.gh24375;
+
+import org.springframework.stereotype.Component;
+
+@Component
+@EnclosingAnnotation(nested2 = @NestedAnnotation)
+public class AnnotatedComponent {
+}