lock screen: clear password after 30s idle with wiggle

shell/lock/LockSurface.qml

@@ -239,6 +239,27 @@ WlSessionLockSurface {
         }
     }
 
+    // Clear password after idle - wiggle then clear
+    Timer {
+        id: _clearTimer
+        interval: 30000
+        running: _keyInput.text.length > 0 && root.auth.state !== "busy"
+        onTriggered: {
+            if (!S.Theme.reducedMotion)
+                _shakeAnim.restart();
+            _keyInput.text = "";
+        }
+    }
+
+    // Restart clear timer on each keystroke
+    Connections {
+        target: _keyInput
+        function onTextChanged() {
+            if (_keyInput.text.length > 0)
+                _clearTimer.restart();
+        }
+    }
+
     // Unlock animation
     property bool _unlocking: false