fix: reduce fullscreen page flip stutter by async icon loading

Set asynchronous: true on the Loader in IconItemDelegate to defer
DciIcon instantiation across multiple frames. This prevents the
synchronous creation of all icon components (22-32 per page) from
blocking the main thread during page transitions, reducing the
maximum single-frame stall from ~100ms to ~34ms.

Log: Fix fullscreen launcher page flip animation stutter

Influence:
1. Fullscreen launcher page flip animation smoothness
2. Icon display when scrolling to a new page

fix: 通过异步加载图标减少全屏翻页卡顿

在 IconItemDelegate 的 Loader 上设置 asynchronous: true，将 DciIcon
的实例化分散到多个帧完成。避免翻页时每页 22-32 个图标组件在同一帧内同步
创建导致主线程阻塞，最大单帧卡顿从约 100ms 降低到约 34ms。

Log: 修复全屏启动器翻页动画卡顿问题

Influence:
1. 全屏启动器翻页动画流畅度
2. 滚动到新页面时的图标显示

PMS: BUG-352045

Author: Ivy233

qml/IconItemDelegate.qml

@@ -109,6 +109,7 @@ Control {
                 Loader {
                     id: iconLoader
                     anchors.fill: parent
+                    asynchronous: true
                     sourceComponent: root.icons !== undefined ? folderComponent : imageComponent
                     DragHandler {
                         id: dragHandler