fix: adjust scrollbar visibility based on system theme policy

Changed the scrollbar visibility initialization logic in ChameleonStyle
to respect system theme's scrollbar policy. Previously, scrollbars were
always set to visible by default, then hidden via animation. Now, when
the system theme specifies Qt::ScrollBarAsNeeded policy, scrollbars
start as invisible; otherwise, they remain visible by default.
This ensures proper scrollbar behavior alignment with user's system
preferences.

fix: 根据系统主题策略调整滚动条可见性

修改了ChameleonStyle中滚动条可见性的初始化逻辑，以遵循系统主题的滚动条
策略。之前滚动条始终默认设置为可见，然后通过动画隐藏。现在，当系统主题指
定Qt::ScrollBarAsNeeded策略时，滚动条初始为不可见；其他情况下保持默认可
见。这确保了滚动条行为与用户系统偏好设置的一致性。

PMS: BUG-339051

Author: mhduiy

styleplugins/chameleon/chameleonstyle.cpp

@@ -4623,8 +4623,16 @@ void ChameleonStyle::resetAttribute(QWidget *w, bool polish)
     w->setAttribute(Qt::WA_Hover, enableHover);
 
     if (auto scrollbar = qobject_cast<QScrollBar *>(w)) {
-        // 默认初始显示滚动条，然后启动隐藏动画
-        scrollbar->setProperty("_d_dtk_scrollbar_visible", true);
+        // 默认按需显示时不显示滚动条，其余情况默认显示，然后启动隐藏动画
+        DPlatformTheme *theme = DGuiApplicationHelper::instance()->systemTheme();
+        if (theme && theme->isValid()) {
+            int sb = theme->scrollBarPolicy();
+            if (sb == Qt::ScrollBarAsNeeded) {
+                scrollbar->setProperty("_d_dtk_scrollbar_visible", false);
+            } else {
+                scrollbar->setProperty("_d_dtk_scrollbar_visible", true);
+            }
+        }
         scrollbar->setAttribute(Qt::WA_OpaquePaintEvent, !polish);
     }
 }