Port 'Save File' demo to Vala (#169)

Author: BharatAtbrat

src/Save File/main.vala

@@ -0,0 +1,32 @@
+#! /usr/bin/env -S vala workbench.vala --pkg gtk4
+
+async void save_file () {
+    var file_dialog = new Gtk.FileDialog () {
+        initial_name = "Workbench.txt"
+    };
+    try {
+        File file = yield file_dialog.save (workbench.window, null);
+
+        uint8[] contents = ("Hello from Workbench!").data;
+
+        yield file.replace_contents_async (contents, // contents
+            null, // etag
+            false, // make_backup
+            FileCreateFlags.NONE, // flags
+            null, // cancellable
+            null // callback
+        );
+
+        message (@"File $(file.get_basename()) saved");
+    } catch (Error e) {
+        message (@"$(e.message)");
+    }
+}
+
+public void main () {
+    var button = (Gtk.Button) workbench.builder.get_object ("button");
+
+    button.clicked.connect (() => {
+        save_file.begin ();
+    });
+}