Fix toString of JarArchive

It returns the absolute path of the jar file instead of '/'

compiler/src/dotty/tools/io/JarArchive.scala

@@ -10,11 +10,13 @@ import scala.jdk.CollectionConverters.*
  * This class implements an [[AbstractFile]] backed by a jar
  * that be can used as the compiler's output directory.
  */
-class JarArchive private (root: Directory) extends PlainDirectory(root) {
+class JarArchive private (val jarPath: Path, root: Directory) extends PlainDirectory(root) {
   def close(): Unit = this.synchronized(jpath.getFileSystem().close())
   override def exists: Boolean = jpath.getFileSystem().isOpen() && super.exists
   def allFileNames(): Iterator[String] =
     java.nio.file.Files.walk(jpath).iterator().asScala.map(_.toString)
+
+  override def toString: String = jarPath.toString
 }
 
 object JarArchive {
@@ -40,6 +42,6 @@ object JarArchive {
       }
     }
     val root = fs.getRootDirectories().iterator.next()
-    new JarArchive(Directory(root))
+    new JarArchive(path, Directory(root))
   }
 }