Support java.nio.file Paths and FileSystems with nested jars

Add a `NestedFileSystemProvider` implementation so that the JDK's
`ZipFileSystem` can load content from nested jars and nested
directory entries.

Creating a `ZipFileSystem` may be a relatively expensive operation as
zip structures need to be parsed and in the case of directory entries
a virtual datablock nees to be generated on the fly. As such, we
install the `ZipFileSystem` as late as possible since in a typical
application it may never be needed.

This commit also tweaks Gradle and Maven plugins to ensure that the
service loader file is written to repackaged jars.

Closes gh-7161

spring-boot-project/spring-boot-tools/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/AbstractJarWriter.java

@@ -220,7 +220,7 @@ public abstract class AbstractJarWriter implements LoaderClassesWriter {
 		try (JarInputStream inputStream = new JarInputStream(new BufferedInputStream(loaderJar.openStream()))) {
 			JarEntry entry;
 			while ((entry = inputStream.getNextJarEntry()) != null) {
-				if (isDirectoryEntry(entry) || isClassEntry(entry)) {
+				if (isDirectoryEntry(entry) || isClassEntry(entry) || isServicesEntry(entry)) {
 					writeEntry(new JarArchiveEntry(entry), new InputStreamEntryWriter(inputStream));
 				}
 			}
@@ -235,6 +235,10 @@ public abstract class AbstractJarWriter implements LoaderClassesWriter {
 		return entry.getName().endsWith(".class");
 	}
 
+	private boolean isServicesEntry(JarEntry entry) {
+		return !entry.isDirectory() && entry.getName().startsWith("META-INF/services/");
+	}
+
 	private void writeEntry(JarArchiveEntry entry, EntryWriter entryWriter) throws IOException {
 		writeEntry(entry, null, entryWriter, UnpackHandler.NEVER);
 	}