Add default handler for screen edge based activation

This change adds a default handle for screen edge based activation in
order to reduce the amount of boilerplate in client sub-classes that do
not support features such as auto-hiding, e.g. popups.

abstract_client.cpp

@@ -3474,4 +3474,9 @@ void AbstractClient::setNoBorder(bool set)
     qCWarning(KWIN_CORE, "%s doesn't support setting decorations", metaObject()->className());
 }
 
+void AbstractClient::showOnScreenEdge()
+{
+    qCWarning(KWIN_CORE, "%s doesn't support screen edge activation", metaObject()->className());
+}
+
 }

abstract_client.h

@@ -764,7 +764,7 @@ public:
      * The AbstractClient also gets raised (e.g. Panel mode windows can cover) and the AbstractClient
      * gets informed in a window specific way that it is shown and raised again.
      */
-    virtual void showOnScreenEdge() = 0;
+    virtual void showOnScreenEdge();
 
     QByteArray desktopFileName() const {
         return m_desktopFileName;

internal_client.cpp

@@ -384,10 +384,6 @@ void InternalClient::updateDecoration(bool check_workspace_pos, bool force)
     }
 }
 
-void InternalClient::showOnScreenEdge()
-{
-}
-
 void InternalClient::destroyClient()
 {
     markAsZombie();

internal_client.h

@@ -65,7 +65,6 @@ public:
     bool takeFocus() override;
     void setNoBorder(bool set) override;
     void updateDecoration(bool check_workspace_pos, bool force = false) override;
-    void showOnScreenEdge() override;
     void destroyClient() override;
 
     void present(const QSharedPointer<QOpenGLFramebufferObject> fbo);

xdgshellclient.cpp

@@ -2012,10 +2012,6 @@ void XdgPopupClient::closeWindow()
 {
 }
 
-void XdgPopupClient::showOnScreenEdge()
-{
-}
-
 bool XdgPopupClient::supportsWindowRules() const
 {
     return false;

xdgshellclient.h

@@ -246,7 +246,6 @@ public:
     QRect transientPlacement(const QRect &bounds) const override;
     bool isCloseable() const override;
     void closeWindow() override;
-    void showOnScreenEdge() override;
     bool wantsInput() const override;
     bool takeFocus() override;
     bool supportsWindowRules() const override;