Add support for TargetDefinition#implicitDependencies

PDE has support for implicitDependencies defined in the target that
Tycho currently ignores.

This adds the required support to Tycho to understand dependencies
defined in this way.

tycho-core/src/main/java/org/eclipse/tycho/core/TargetPlatformConfiguration.java

@@ -29,10 +29,13 @@
 import java.util.Map;
 import java.util.Set;
 import java.util.function.Supplier;
+import java.util.stream.Stream;
 
 import org.codehaus.plexus.util.xml.Xpp3Dom;
 import org.eclipse.equinox.p2.metadata.IRequirement;
 import org.eclipse.tycho.ArtifactKey;
+import org.eclipse.tycho.ArtifactType;
+import org.eclipse.tycho.DefaultArtifactKey;
 import org.eclipse.tycho.OptionalResolutionAction;
 import org.eclipse.tycho.TargetEnvironment;
 import org.eclipse.tycho.core.resolver.shared.IncludeSourceMode;
@@ -267,7 +270,9 @@ public DependencyResolverConfiguration getDependencyResolverConfiguration() {
 
     @Override
     public List<ArtifactKey> getAdditionalArtifacts() {
-        return extraRequirements;
+        Stream<DefaultArtifactKey> targetFiles = getTargets().stream().flatMap(tdf -> tdf.implicitDependencies())
+                .map(id -> new DefaultArtifactKey(ArtifactType.TYPE_ECLIPSE_PLUGIN, id.getId()));
+        return Stream.concat(extraRequirements.stream(), targetFiles).distinct().toList();
     }
 
     @Override

tycho-targetplatform/src/main/java/org/eclipse/tycho/targetplatform/TargetDefinition.java

@@ -21,6 +21,7 @@
 import java.util.Collection;
 import java.util.List;
 import java.util.Properties;
+import java.util.stream.Stream;
 
 import org.eclipse.tycho.IArtifactFacade;
 import org.eclipse.tycho.MavenArtifactRepositoryReference;
@@ -54,9 +55,21 @@ public interface TargetDefinition {
 	@Override
 	public boolean equals(Object obj);
 
+	/**
+	 * 
+	 * @return a stream of implicit dependencies defined in the target to add as an
+	 *         additional dependency to every project
+	 */
+	Stream<ImplicitDependency> implicitDependencies();
+
 	@Override
 	public int hashCode();
 
+	public interface ImplicitDependency {
+
+		String getId();
+	}
+
 	public interface Location {
 
 		/**