Use parent width rather than fixed width

When the action buttons are too wide, it causes the text box to be that wide, since the `Input` has `Layout.fillWidth: true` set, causing the text to overflow the background. This change makes the background expand with the text.

kde/sddm/components/Input.qml

@@ -12,10 +12,10 @@ TextField {
         color: "#1E2326"
         opacity: 0.7
         radius: parent.width / 2
-        height: 30
-        width: 270
+        width: parent.width
+        height: width / 9
         border.width: 1
         border.color: "#121517"
         anchors.centerIn: parent
     }
-}
+}