GH-1066 - Provide abstraction to access ApplicationModuleIdentifiers in order of module dependency.

Introduce ApplicationModuleIdentifiers as abstraction for an ordered collection of application module identifiers.

Introduced ApplicationModuleMetadata as abstraction for the generated metadata (usually located in META-INF/spring-modulith/application-modules.json) to expose the information we currently need to downstream infrastructure components. Migrated the components introduced to execute ApplicationModuleInitializers to AMA and adapt auto-configuration accordingly.

spring-modulith-core/src/main/java/org/springframework/modulith/core/ApplicationModuleIdentifiers.java

@@ -0,0 +1,88 @@
+/*
+ * Copyright 2025 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.modulith.core;
+
+import java.util.Iterator;
+import java.util.List;
+import java.util.function.Supplier;
+import java.util.stream.Stream;
+
+import org.springframework.util.Assert;
+
+/**
+ * {@link ApplicationModuleIdentifier}s that allow iteration in the order provided by the sources.
+ *
+ * @author Oliver Drotbohm
+ * @since 1.4
+ */
+public class ApplicationModuleIdentifiers implements Iterable<ApplicationModuleIdentifier> {
+
+	private final Supplier<Stream<ApplicationModuleIdentifier>> source;
+
+	/**
+	 * Creates a new {@link ApplicationModuleIdentifiers} instance for the given source.
+	 *
+	 * @param source must not be {@literal null}.
+	 */
+	private ApplicationModuleIdentifiers(Supplier<Stream<ApplicationModuleIdentifier>> source) {
+
+		Assert.notNull(source, "Source must not be null!");
+
+		this.source = source;
+	}
+
+	/**
+	 * Creates a new {@link ApplicationModuleIdentifiers} from the given ApplicationModules.
+	 *
+	 * @param modules must not be {@literal null}.
+	 * @return will never be {@literal null}.
+	 */
+	public static ApplicationModuleIdentifiers of(ApplicationModules modules) {
+
+		Assert.notNull(modules, "ApplicationModules must not be null!");
+
+		return new ApplicationModuleIdentifiers(() -> modules.stream()
+				.map(ApplicationModule::getIdentifier));
+	}
+
+	/**
+	 * Creates a new {@link ApplicationModuleIdentifiers} for the given source identifiers.
+	 *
+	 * @param identifiers will never be {@literal null}.
+	 * @return will never be {@literal null}.
+	 */
+	public static ApplicationModuleIdentifiers of(List<ApplicationModuleIdentifier> identifiers) {
+		return new ApplicationModuleIdentifiers(() -> identifiers.stream());
+	}
+
+	/**
+	 * Creates a new {@link Stream} of {@link ApplicationModuleIdentifier}s.
+	 *
+	 * @return will never be {@literal null}.
+	 */
+	public Stream<ApplicationModuleIdentifier> stream() {
+		return source.get();
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see java.lang.Iterable#iterator()
+	 */
+	@Override
+	public Iterator<ApplicationModuleIdentifier> iterator() {
+		return stream().iterator();
+	}
+}