fix(ComboBox): fix the issue of highlighted state lingering after

mouse leaves menu items

Root cause: The delegate.highlighted is bound to
control.highlightedIndex (read-only).
When the mouse leaves the popup area, this value is not automatically
reset, causing the highlighted state to persist.

Fix approach:
- Add a new contentHovered property to the popup to track whether
the mouse is within the popup list area
- Use HoverHandler in Qt6 to synchronize the contentHovered state
- Use MouseArea (acceptedButtons: Qt.NoButton) in Qt5 to synchronize
the contentHovered state
- Change delegate.highlighted to popup.contentHovered &&
control.highlightedIndex === index

Log: Fixed the issue of lingering highlight on ComboBox menu items after mouse leaves
Influence: ComboBox menu items

fix(ComboBox): 修复菜单项鼠标离开后高亮残留问题

根因：delegate.highlighted 绑定 control.highlightedIndex（只读），
鼠标离开弹出区域时该值不会自动重置，导致高亮状态持续残留。

修复方案：
- 为 popup 新增 contentHovered 属性，追踪鼠标是否在弹出列表区域内
- Qt6 版本使用 HoverHandler 同步 contentHovered 状态
- Qt5 版本使用 MouseArea（acceptedButtons: Qt.NoButton）同步 contentHovered 状态
- 将 delegate.highlighted 改为 popup.contentHovered && control.highlightedIndex === index

Log: 修复ComboBox的菜单项鼠标离开后高亮残留问题
Influence: ComboBox菜单项
PMS: BUG-306683

Author: electricface

qt6/src/qml/ComboBox.qml

@@ -36,7 +36,7 @@ T.ComboBox {
         useIndicatorPadding: true
         text: control.textRole ? (Array.isArray(control.model) ? modelData[control.textRole] : (model[control.textRole] === undefined ? modelData[control.textRole] : model[control.textRole])) : modelData
         icon.name: (control.iconNameRole && model[control.iconNameRole] !== undefined) ? model[control.iconNameRole] : null
-        highlighted: control.highlightedIndex === index
+        highlighted: popup.contentHovered && control.highlightedIndex === index
         hoverEnabled: control.hoverEnabled
         autoExclusive: true
         checked: control.currentIndex === index
@@ -169,13 +169,17 @@ T.ComboBox {
         rightMargin: DS.Style.popup.margin
         palette: control.palette
         implicitWidth: control.flat ? Math.max(contentItem.implicitWidth, control.width) : control.width
+        property bool contentHovered: false
         contentItem: ArrowListView {
             clip: true
             maxVisibleItems: control.maxVisibleItems
             view.model: control.delegateModel
             view.currentIndex: control.highlightedIndex
             view.highlightRangeMode: ListView.ApplyRange
             view.highlightMoveDuration: 0
+            HoverHandler {
+                onHoveredChanged: popup.contentHovered = hovered
+            }
         }
 
         background: FloatingPanel {