Introduce ReflectiveScan

This commit allows `@Reflective` to be used on arbitrary types, not
only Spring beans. This makes the feature much more powerful as
components can be tagged directly.

Scanning happens during AOT processing (typically at build-time) when
`@ReflectiveScan` is used. Types do not need to have a particular
annotation, and types that can't be loaded are ignored.

This commit also exposes the infrastructure that does the scanning so
that custom code can do the scanning in an AOT contribution if they
don't want to rely on the annotation.

Closes gh-33132

framework-docs/src/main/java/org/springframework/docs/core/aot/hints/reflective/MyConfiguration.java

@@ -0,0 +1,25 @@
+/*
+ * 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.docs.core.aot.hints.reflective;
+
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.ReflectiveScan;
+
+@Configuration
+@ReflectiveScan("com.example.app")
+public class MyConfiguration {
+}