UseJava: Add RESOURCES with NAMESPACE to add_jar()

add_jar() currently requires (undocumented) that resources be supplied
as relative paths.  The resources *may* then end up in a path which does
not reflect the original path particularly when performing out-of-source
builds.  This change adds a RESOURCE (and NAMESPACE) parameter and a
function to add the names resources into the named namespace within the
jar- and thus address both of these problems.

Fixes: #22101

Tests/Java/ResourceNS.java

@@ -0,0 +1,48 @@
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.io.BufferedReader;
+import java.io.IOException;
+
+class ResourceNS
+{
+    public static void main(String args[])
+    {
+        ResourceNS res = new ResourceNS();
+        res.displayResourceText();
+    }
+
+    public void displayResourceText()
+    {
+        /*
+         * Since Java SE 9, invoking getResourceXXX on a class in a named
+         * module will only locate the resource in that module, it will
+         * not search the class path as it did in previous release. So when
+         * you use Class.getClassLoader().getResource() it will attempt to
+         * locate the resource in the module containing the ClassLoader,
+         * possibly something like:
+         *      jdk.internal.loader.ClassLoaders.AppClassLoader
+         * which is probably not the module that your resource is in, so it
+         * returns null.
+         *
+         * You have to make java 9+ search for the file in your module.
+         * Do that by changing Class to any class defined in your module in
+         * order to make java use the proper class loader.
+        */
+
+        // Namespaces are relative, use leading '/' for full namespace
+        InputStream is =
+            ResourceNS.class.getResourceAsStream("/ns/ns1/HelloWorld.txt");
+        // C++:    cout << is.readline();    // oh, well !
+        InputStreamReader isr = new InputStreamReader(is);
+        BufferedReader reader = new BufferedReader(isr);
+        String out = "";
+        try{
+            out = reader.readLine();
+        } catch(IOException e) {
+            e.printStackTrace();
+            System.out.println(e);
+        }
+
+        System.out.println(out);
+    }
+}