feat(lockscreen): enable use of videos as screensaver in the lock screen (#1819)

* feat(lockscreen): enable use of videos as screensaver in the lock screen

* reducing debug logs

* feature becomes available only when QtMultimedia is available

quickshell/Services/MultimediaService.qml

@@ -0,0 +1,35 @@
+pragma Singleton
+pragma ComponentBehavior: Bound
+
+import QtQuick
+import Quickshell
+
+Singleton {
+    id: root
+
+    property bool available: false
+
+    function detectAvailability() {
+        try {
+            const testObj = Qt.createQmlObject(`
+                import QtQuick
+                import QtMultimedia
+                Item {}
+            `, root, "MultimediaService.TestComponent");
+            if (testObj) {
+                testObj.destroy();
+            }
+            available = true;
+            return true;
+        } catch (e) {
+            available = false;
+            return false;
+        }
+    }
+
+    Component.onCompleted: {
+        if (!detectAvailability()) {
+            console.warn("MultimediaService: QtMultimedia not available");
+        }
+    }
+}