Port 'Power Profile Monitor' demo to Vala (#164)

src/Power Profile Monitor/main.vala

@@ -0,0 +1,19 @@
+#! /usr/bin/env -S vala workbench.vala --pkg libadwaita-1
+
+public void main () {
+    var overlay = (Adw.ToastOverlay) workbench.builder.get_object ("overlay");
+    var power_profile_monitor = PowerProfileMonitor.dup_default ();
+
+    power_profile_monitor.notify["power-saver-enabled"].connect (() => {
+        var toast = new Adw.Toast ("power-saver") {
+            priority = Adw.ToastPriority.HIGH
+        };
+
+        if (power_profile_monitor.power_saver_enabled) {
+            toast.title = "Power Saver Enabled";
+        } else {
+            toast.title = "Power Saver Disabled";
+        }
+        overlay.add_toast (toast);
+    });
+}