fix: correct bubble position on cold start

1. Set explicit implicitWidth and implicitHeight for appIcon in
   NotifyItemContent
2. Prevent icon size from being incorrectly resolved during initial
   layout, which caused wrong bubble height calculation
3. Ensure bubble popup position is correct on cold start

Log: Fix bubble position error caused by incorrect height calculation on cold start

fix: 修复冷启动时气泡弹出位置错误

1. 为 NotifyItemContent 中的 appIcon 设置显式的 implicitWidth 和
   implicitHeight
2. 防止图标在初始布局时尺寸解析错误，导致气泡高度计算不对
3. 确保冷启动时气泡弹出位置正确

Log: 修复冷启动时因高度计算错误导致气泡弹出位置不对的问题
PMS: BUG-362143

Author: MyLeeJiEun

panels/notification/plugin/NotifyItemContent.qml

@@ -202,6 +202,8 @@ NotifyItem {
                 id: appIcon
                 name: root.iconName !== "" ? root.iconName : "application-x-desktop"
                 sourceSize: Qt.size(24, 24)
+                implicitWidth: 24
+                implicitHeight: 24
                 Layout.alignment: Qt.AlignLeft | Qt.AlignTop
                 Layout.topMargin: 8
                 Layout.leftMargin: 10