Port Loading.qml to LoadingPlaceholder

BUG: 456629

src/qml/Component/Login/Loading.qml

@@ -5,23 +5,15 @@ import QtQuick 2.15
 import QtQuick.Controls 2.15 as QQC2
 import QtQuick.Layouts 1.15
 
-import org.kde.kirigami 2.15 as Kirigami
+import org.kde.kirigami 2.20 as Kirigami
 
 import org.kde.neochat 1.0
 
-Kirigami.PlaceholderMessage {
+Kirigami.LoadingPlaceholder {
     property var showContinueButton: false
     property var showBackButton: false
-    property string title: i18n("Loading…")
-
-    anchors.centerIn: parent
 
     QQC2.Label {
         text: i18n("Please wait. This might take a little while.")
     }
-
-    QQC2.BusyIndicator {
-        Layout.alignment: Qt.AlignHCenter
-        running: false
-    }
 }