Add multi-release processing support

Currently bnd is not a capable of processing multi-release jars, this
adds support of multi-release processing by a new directive -release
where one can select what release version should be processed by bnd.

Fixes bndtools#5346

biz.aQute.bndlib/src/aQute/bnd/osgi/Jar.java

@@ -1338,7 +1338,7 @@ public void removeSubDirs(String dir) {
 	}
 
 	private static final Predicate<String>	pomXmlFilter	= new PathSet("META-INF/maven/*/*/pom.xml").matches();
-	private int								release;
+	private int								release			= -1;
 
 	public Stream<Resource> getPomXmlResources() {
 		return getResources(pomXmlFilter);

biz.aQute.bndlib/test/aQute/bnd/build/JarTest.java

@@ -0,0 +1,70 @@
+package aQute.bnd.build;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.File;
+import java.util.Collections;
+import java.util.Set;
+import java.util.jar.JarEntry;
+import java.util.jar.JarFile;
+import java.util.stream.Collectors;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+import aQute.bnd.osgi.Jar;
+import aQute.bnd.osgi.Resource;
+
+public class JarTest {
+
+	private static final String	TEST_CLASS_PATH		= "a/test/package/Test.class";
+
+	private static final String	VERSIONED_TEST_CLASS_PATH	= "META-INF/versions/9/" + TEST_CLASS_PATH;
+
+	@TempDir
+	File						tempDir;
+
+	@Test
+	public void testMultiReleaseJar() throws Exception {
+		File jarfile = new File(tempDir, "packed.jar");
+		try (Jar jar = new Jar("testme")) {
+			jar.ensureManifest();
+			Resource java8Class = resource();
+			Resource java9Class = resource();
+			jar.putResource(TEST_CLASS_PATH, java8Class);
+			jar.putResource(VERSIONED_TEST_CLASS_PATH, java9Class);
+			// without a release, content must be returned as-is
+			assertEquals(java8Class, jar.getResource(TEST_CLASS_PATH));
+			assertEquals(java9Class, jar.getResource(VERSIONED_TEST_CLASS_PATH));
+			// with a release set below 9 we should only see the default content
+			jar.setRelease(0);
+			assertEquals(java8Class, jar.getResource(TEST_CLASS_PATH));
+			assertNull(jar.getResource(VERSIONED_TEST_CLASS_PATH));
+			// with release 9 set, we now should see the java 9 content
+			jar.setRelease(9);
+			assertEquals(java9Class, jar.getResource(TEST_CLASS_PATH));
+			// if we write the jar out, all content should be present
+			jar.writeFolder(tempDir);
+			File defaultFile = new File(tempDir, TEST_CLASS_PATH);
+			assertTrue(defaultFile.isFile(), defaultFile.getAbsolutePath() + " is missing");
+			File versionedFile = new File(tempDir, VERSIONED_TEST_CLASS_PATH);
+			assertTrue(versionedFile.isFile(), versionedFile.getAbsolutePath() + " is missing");
+			jar.write(jarfile);
+		}
+		try (JarFile jar = new JarFile(jarfile)) {
+			Set<String> collect = Collections.list(jar.entries())
+				.stream()
+				.map(JarEntry::getName)
+				.collect(Collectors.toSet());
+			assertTrue(collect.contains(TEST_CLASS_PATH));
+			assertTrue(collect.contains(VERSIONED_TEST_CLASS_PATH));
+		}
+	}
+
+	private Resource resource() {
+		return new aQute.bnd.osgi.EmbeddedResource(new byte[0], System.currentTimeMillis());
+	}
+
+}