quick: Make dealing with window flags more stable

There's only one place where we need to set the flags, it's when
creating the FloatingWindowQuick. So no need to complex machinery
which is bug propne

src/private/quick/QWidgetAdapter_quick.cpp

@@ -31,7 +31,7 @@ using namespace KDDockWidgets;
 
 QWidgetAdapter::QWidgetAdapter(QQuickItem *parent, Qt::WindowFlags flags)
     : QQuickItem(parent)
-    , m_requestedWindowFlags(flags)
+    , m_windowFlags(flags)
 {
     this->setParent(parent); // also set parentItem
 
@@ -291,18 +291,6 @@ void QWidgetAdapter::setParent(QQuickItem *p)
 {
     QQuickItem::setParent(p);
     QQuickItem::setParentItem(p);
-
-    if (m_requestedWindowFlags) {
-        // With QtWidgets, when we create a QWidget it creates the QWindow immediately,
-        //so the flags are passed from QWidget to QWindow in one go. But with QtQuick this needs to
-        //be done in two steps. Our FloatingWindow is a QQuickItem, when it gets a window, we
-        // set the flags that were requested
-
-        if (QWindow *w = windowHandle()) {
-            w->setFlags(m_requestedWindowFlags);
-            m_requestedWindowFlags = {};
-        }
-    }
 }
 
 void QWidgetAdapter::activateWindow()
@@ -328,10 +316,7 @@ QSize QWidgetAdapter::sizeHint() const
 
 Qt::WindowFlags QWidgetAdapter::windowFlags() const
 {
-    if (QWindow *w = windowHandle())
-        return w->flags();
-
-    return m_requestedWindowFlags;
+    return m_windowFlags;
 }
 
 /** static */
@@ -373,15 +358,10 @@ void QWidgetAdapter::makeItemFillParent(QQuickItem *item)
 
 void QWidgetAdapter::setFlag(Qt::WindowType f, bool on)
 {
-    if (QWindow *w = windowHandle()) {
-        w->setFlag(f, on);
+    if (on) {
+        m_windowFlags |= f;
     } else {
-        // When we create a QWindow we'll set these
-        if (on) {
-            m_requestedWindowFlags |= f;
-        } else {
-            m_requestedWindowFlags &= ~f;
-        }
+        m_windowFlags &= ~f;
     }
 }