[wayland] Add a bool ShellClient::isInternal

Helper method to identify whether a ShellClient is for one of KWin's
internal connections (e.g. a QWindow).

shell_client.cpp

@@ -377,4 +377,10 @@ void ShellClient::updateInternalWindowGeometry()
     setGeometry(m_internalWindow->geometry());
 }
 
+bool ShellClient::isInternal() const
+{
+    return m_shellSurface->client() == waylandServer()->internalConnection() ||
+           m_shellSurface->client() == waylandServer()->qtConnection();
+}
+
 }

shell_client.h

@@ -90,6 +90,7 @@ public:
     quint32 windowId() const {
         return m_windowId;
     }
+    bool isInternal() const;
 
 protected:
     void addDamage(const QRegion &damage) override;