Add getAdditionalEntries to IClasspathContributor

Adds a new method to allow classpath contributor to append additional
classpath entries at the end of the calculation process.

Author: steffenschmitt1

ui/org.eclipse.pde.core/src/org/eclipse/pde/core/IClasspathContributor.java

@@ -83,6 +83,7 @@ public interface IClasspathContributor {
 	 * @return additional classpath entries to add to the project at the end of
 	 *         the classpath calculation, possibly empty, must not be
 	 *         <code>null</code>
+	 * @since 3.21.0
 	 */
 	default List<IClasspathEntry> getAdditionalEntries(BundleDescription project) {
 		return List.of();