scene: Ignore xwayland window shape

The shape region is used to clip the window contents. But, in practice,
it's used by a few applications. The most notable is xeyes.

The APIs that the shape region requires are manageable, but it would be
much preferred if we had a much simpler design.

In terms of the shape region support on Wayland, it's not widely
supported across all wayland compositors, to my knowledge, only two
support it, some compositors even want to disable XSHAPE extension at all.

This change makes the Xwayland windows ignore the shape region to see if
any real world applications are affected by it. If not, then we could
safely simplify the scene bits later.

The Xorg session is unaffected by this change.

src/scene/surfaceitem_wayland.cpp

@@ -252,30 +252,15 @@ SurfaceItemXwayland::SurfaceItemXwayland(X11Window *window, Item *parent)
     : SurfaceItemWayland(window->surface(), parent)
     , m_window(window)
 {
-    connect(window, &X11Window::shapeChanged, this, &SurfaceItemXwayland::discardQuads);
-}
-
-QList<QRectF> SurfaceItemXwayland::shape() const
-{
-    QList<QRectF> shape = m_window->shapeRegion();
-    for (QRectF &shapePart : shape) {
-        shapePart = shapePart.intersected(rect());
-    }
-    return shape;
 }
 
 QRegion SurfaceItemXwayland::opaque() const
 {
-    QRegion shapeRegion;
-    for (const QRectF &shapePart : shape()) {
-        shapeRegion += shapePart.toRect();
-    }
     if (!m_window->hasAlpha()) {
-        return shapeRegion;
+        return rect().toRect();
     } else {
-        return m_window->opaqueRegion() & shapeRegion;
+        return m_window->opaqueRegion() & rect().toRect();
     }
-    return QRegion();
 }
 #endif
 } // namespace KWin

src/scene/surfaceitem_wayland.h

@@ -95,7 +95,6 @@ public:
     explicit SurfaceItemXwayland(X11Window *window, Item *parent = nullptr);
 
     QRegion opaque() const override;
-    QList<QRectF> shape() const override;
 
 private:
     X11Window *m_window;